BIOLOGY 

LIBRARY 

G 


BACTERIA,  YEASTS,  AND  MOLDS 
IN  THE  HOME 


BY 


H.  W.  CONN,  PH.D. 


PROFESSOR  OF  BIOLOGY  IN  WESLEYAN  UNIVERSITY,  MIDDLETOWN,  CONN. 

ATITHOR  OF  "AGRICULTURAL  BACTERIOLOGY,"  "  BACTERIA  IN 

MILK  AND  ITS  PRODUCTS,"  "THE  STORY  OF  GERM 

LIFE,"  "THE  METHOD  OF  EVOLUTION,"  ETC. 


GINN   &   COMPANY 

BOSTON  •  NEW  YORK  •  CHICAGO  •  LONDON 


ENTERED  AT  STATIONERS'  HALL 


COPYRIGHT,  1903 
BY   H.  W.  CONN 


ALL    RIGHTS    RESERVED 


Cfte   fltbenaum 

GINN   &  COMPANY  •  PRO- 
PRIETORS •  BOSTON  •  U.S.A. 


C£ 

BIOLOGY 

LIBRARY 

G 


PREFACE 

The  rapidly  growing  interest  in  home  economics  is  caus- 
ing this  subject  slowly  to  assume  the  aspect  of  an  exact 
science.  At  the  present  time  it  is  becoming  necessary 
for  those  expecting  to  become  housewives  to  understand 
at  least  the  elementary  phases  of  a  number  of  sciences, 
most  prominent  among  which  are  chemistry  and  bacteri- 
ology. The  relation  of  microorganisms  to  household  affairs 
has  only  been  recognized  in  the  last  few  years,  but  is 
now  felt  to  be  one  of  the  most  important  phases  in  the 
study  of  the  problems  of  the  household.  The  present 
work  is  therefore  designed  for  all  interested  in  household 
affairs,  including  not  only  students  of  household  econom- 
ics but  all  persons  who  have  practical  charge  of  homes 
and  are  interested  in  keeping  them  in  the  best  and  most 
healthful  condition. 


238904 

iii 


TABLE    OF    CONTENTS 


CHAPTER 

I.    INTRODUCTION 


PAGE 
I 


SECTION  I  — MOLDS 

II.    THE  GENERAL  NATURE  OF  MOLDS       .        .        .  12 

III.  CONDITIONS  FAVORING  MOLD  GROWTH     .     '.  .        .      32 

IV.  THE    DECAY    OF    FRUIT;    USEFUL    MOLDS;    MOLD 

DISEASES          .        .        *        ,        .        »        .          40 


SECTION  II— YEASTS 

V.    YEASTS  AND  THEIR  DISTRIBUTION     . 
VI.    YEASTS  IN  THE  HOUSEHOLD. 
VII.    BREAD  RAISING;  FERMENTED  LIQUORS    . 


56 
68 
86 


SECTION  III  — BACTERIA 

VIII.    THE  GENERAL  NATURE  OF  BACTERIA  .         .         .  100 

IX.    BACTERIA  WHICH  LIVE  UPON  DEAD  FOOD       .  .     124 

X.   THE  PRESERVATION  OF  FOOD;  DRYING;  COOLING  139 

XL   THE  USE  OF  PRESERVATIVES    .        V        .        .  .     157 

XII.    PRESERVATION  BY  CANNING  .        .        ...        .  169 

XIII.  MILK;  EGGS;  PTOMAINE  POISONING     .  ...      .  .     182 

XIV.  DISEASE  BACTERIA 203 


Vi  CONTENTS 

CHAPTER  PAGE 

XV.    PREVENTION    OF    DISTRIBUTION   OF   CONTAGIOUS 

DISEASES     .        ...        .        .        .        .212 

XVI.   PRACTICAL  SUGGESTIONS        .        .        .        .        .  241 

XVII.   DISINFECTION     .        .        .        .        .        .        ."       .  255 

APPENDIX 

DIRECTIONS  FOR  LABORATORY  EXPERIMENTS  .        .        .  267 

INDEX      .                         ........  287 


BACTERIA, 
YEASTS,  AND    MOLDS 


CHAPTER    I 
INTRODUCTION 

Bacteria,  yeasts,  and  molds  comprise  a  series  of  plants 
commonly  known  as  microorganisms,  or  more  popularly  as 
microbes.  It  has  for  some  time  been  recognized  that 
together  they  form  a  group  of  the  utmost  importance 
not  only  to  the  physician  but  also  to  the  agriculturist. 
To-day  it  is  beginning  to  be  appreciated  that  their  rela- 
tion to  the  ordinary  household,  and  hence  to  the  house- 
wife, is  even  more  intimate  than  to  the  physician.  We 
are  learning  that  many  of  the  tasks  of  the  housekeeper, 
some  of  which  may  be  more  or  less  unpleasant,  have  their 
foundation  in  bacteriology,  and  we  are  beginning  to  recog- 
nize that  these  microorganisms  constitute  the  foundation 
of  the  demand  for  cleanliness  so  forcibly  emphasized  in 
modern  times. 

In  the  household  microorganisms  have  an  important 
bearing  in  three  directions  : 

1.  They  are  the  cause  of  the  decay  and  spoiling  of  foods 
and  many  other  products. 

2.  They  are  sometimes  of  value  in  the  preparation  of 
foods. 

3.  They  are  the  cause  of  contagious  diseases. 


2         BACTERIA,  YEASTS,  AND  MOLDS 

i.    MICROORGANISMS  AND  THE  PRESERVATION  OF  FOOD 

Although  household  duties  are  varied  in  character,  the 
larger  part  of  them  concern  the  preparation  and  the  pres- 
ervation of  foods.  The  preparation  of  food  belongs  pri- 
marily to  the  department  of  cooking,  although  certain 
other  factors  are  concerned.  But  the  science  of  cooking 
has  little  to  do  with  the  preservation  of  food.  This  latter 
problem  is  intimately  related  to  modern  bacteriology.  It 
is  largely  for  this  reason  that  the  study  of  bacteriology 
and  kindred  subjects  has  in  recent  years  come  to  be 
looked  upon  as  a  part  of  the  necessary  training  of  the 
housewife. 

At  the  outset  we  may  properly  ask,  Why  is  it  that  food 
spoils?  Why  will  not  food  keep  indefinitely  without  the 
many  contrivances  designed  to  prevent  its  spoiling  ?  The 
answer  to  this  question  is,  briefly,  that  other  living  things 
besides  ourselves  are  fond  of  the  same  foods  of  which  we 
are  fond,  and  that  these  other  living  beings  take  every 
occasion  to  consume  the  material  which  we  design  for  our 
own  food.  Preserving  the  food  in  our  pantries,  cellars, 
and  refrigerators,  therefore,  simply  means  protecting  it 
from  consumption  by  other  living  organisms  ;  and  if  we 
can  keep  these  organisms  away,  food  may  be  indefinitely 
preserved.  On  the  other  hand,  if  we  cannot  protect  our 
food  from  the  attack  of  these  organisms,  it  spoils ;  for  the 
spoiling  of  food  is  simply  the  result  of  its  consumption  by 
living  beings  for  whom  we  have  not  designed  it. 

The  living  beings  that  endeavor  to  consume  our  food 
comprise,  in  the  first  place,  some  of  the  larger  animals 
with  which  every  one  is  familiar.  Every  one  knows  about 


PRESERVATION  OF  FOODS  3 

rats  and  mice,  and  the  various  insects  in  the  home  are 
only  too  familiar  pests.  But  not  every  one  understands 
that  in  addition  to  these  large  animals  there  is  a  great 
host  of  plants  and  animals  which  seize  every  opportunity 
of  feeding  upon  that  which  we  intend  for  our  own  use. 
All  such  small  animals  and  plants  go  by  the  general  name 
of  microbes  or  microorganisms. 

We  are  chiefly  concerned,  in  this  book,  with  three 
important  groups  of  plants,  Some  of  these  plants  are 
large  enough  to  be  seen  easily  and  are  generally  well 
known,  such  as  the  molds  that  occur  everywhere,  and  are 
always  regarded  as  nuisances  in  household  economy.  In 
addition  to  the  visible  plants  there  is  a  still  larger  num- 
ber of  others,  quite  too  small  to  be  visible  to  the  naked 
eye  and,  indeed,  only  seen  with  the  high  powers  of  the 
microscope.  These  invisible  organisms  are  the  smallest 
living  beings  of  which  we  have  any  knowledge,  and  are 
both  friends  and  foes.  Not  only  are  they  invisible  to  the 
naked  eye  but  to  the  ordinary  housewife  they  are  quite 
unknown.  Until  within  recent  years  they  have  been 
unknown  even  to  scientists,  and  although  science  has  now 
learned  to  understand  quite  well  what  they  are  and  what 
they  do,  to  the  public  in  general  they  are  little  more  than 
a  name  around  which  cluster  various  mysteries  and  in 
regard  to  which  there  is  no  general  information.  Molds 
and  yeasts  have  long  been  known.  The  term  bacteria  is  new, 
and  refers  to  organisms  just  beginning  to  claim  public 
attention  but  in  regard  to  which  there  is  at  present  a 
large  amount  of  misunderstanding.  But  even  though 
they  are  very  minute,  and  though  she  knows  little  about 
them,  the  housewife  finds  them  the  most  serious,  indeed 


4  BACTERIA,   YEASTS,  AND    MOLDS 

the  only  serious  foe  with  which  she  has  to  contend  in  her 
attempt  to  keep  food  in  proper  condition  for  use. 

These  invisible  plants  are  constantly  on  the  alert  to  con- 
sume for  themselves  the  foods  which  the  housewife  designs 
for  the  table.  If  they  have  a  chance  to  get  at  the  food, 
she  soon  notices  that  it  undergoes  a  series  of  changes, 
characterized  by  what  we  call  putrefaction,  decay,  souring,  or 
perhaps  some  other  change  not  properly  classed  under 
any  of  these  terms.  The  general  rotting  of  fruit,  the 
decay  of  meat,  the  souring  of  milk,  and  a  host  of  other 
similar  phenomena  which  occur  in  every  pantry  if  the  food 
is  not  carefully  protected,  represent  some  of  the  effects 
produced  in  foods  when  microorganisms  begin  to  feed 
upon  them.  Thus  it  is  evident  that  these  microscopic 
plants  play  a  very  great  part  in  domestic  economy. 
This  fact,  however,  has  not  been  thoroughly  appreciated 
until  recent  years,  and  indeed  it  is  only  just  beginning 
to  be  recognized  to-day  that  the  housewife's  knowledge 
should  comprise  an  understanding  of  the  nature  and  hab- 
itat of  these  microscopic  foes,  their  methods  of  distribu- 
tion from  place  to  place,  the  conditions  under  which  they 
grow  and  fail  to  grow,  together  with  the  various  devices 
which  may  be  adopted  for  checking  their  active  growth 
where  they  are  not  wanted.  Although  the  facts  have 
only  recently  been  appreciated,  it  is  known  to-day  that  a 
very  considerable  part  of  the  duties  in  every  household  is 
concerned  with  these  microscopic  organisms,  known  and 
unknown. 

The  chief  desire  of  the  housewife  is  to  prevent  the 
growth  of  these  microorganisms  in  places  where  they 
are  not  wanted.  For  this  purpose  have  been  invented 


MICROORGANISMS   AS   USEFUL  AGENTS  5 

refrigerators  and  all  devices  for  cold  storage  and  for  cool- 
ing and  keeping  cold  any  food  products  ;  to  this  end,  too, 
are  designed  the  various  methods  of  preserving  food  and 
fruits.  The  immense  industry  of  canning,  either  on  a 
large  scale  as  is  done  in  factories,  or  on  a  small  scale  as 
is  done  in  the  household,  is  dependent  upon  the  relation 
of  microorganisms  to  food.  The  sterilizing  or  pasteuriz- 
ing of  milk,  as  well  as  other  foods,  is  also  a  bacteriological 
problem,  and,  indeed,  many  other  phases  of  household 
life  are  really  bacteriological  phenomena.  Whether  or 
not  she  possesses  a  scientific  knowledge  of  bacteria  and 
their  allies,  the  housewife  must  have  a  certain  practical 
knowledge  of  their  nature  and  of  their  powers,  for  this 
practical  knowledge  is  absolutely  necessary  to  enable  her 
to  preserve  her  food  successfully  from  the  microorganisms 
which  are  so  liable  to  spoil  it. 

2.    MICROORGANISMS  AS  USEFUL  AGENTS 

It  must  not  be  understood,  however,  that  micro- 
organisms are  always  our  foes.  It  is  true  that  in  the 
household  they  are  commonly  a  source  of  trouble,  but 
it  is  also  true  that  some  of  them  are  distinctly  friends. 
To  appreciate  that  they  are  sometimes  useful,  even  in  our 
foods,  one  needs  only  to  remember  that  under  this  head 
are  included  the  great  group  of  yeasts  that  play  such  an 
important  part  in  the  household  in  the  raising  of  bread 
and  in  all  types  of  fermentation.  Yeasts,  as  well  as  bac- 
teria, are  microscopic  plants,  of  which  the  microscopist 
recognizes  many  kinds.  Some  of  these  are  troublesome, 
but,  so  far  as  concerns  their  relations  in  the  household, 


6  BACTERIA,   YEASTS,  AND    MOLDS 

they  are  useful  servants  rather  than  undesirable  foes. 
Even  bacteria,  which  are  in  general  looked  upon  as 
dreaded  foes,  and  as  agents  only  of  evil,  are,  under 
some  circumstances,  our  friends  rather  than  our  enemies. 
Bacteria,  for  example,  produce  the  delicate  flavors  in 
butter  and  the  stronger  but  equally  delicious  flavors  of 
cheese.  Bacteria  also  are  solely  responsible  for  the  man- 
ufacture of  vinegar ;  for  although  vinegar  might  be  made 
by  chemical  means,  the  vinegar  of  our  tables  is  produced 
by  the  agency  of  bacteria.  Molds  also,  though  generally 
looked  upon  as  unmitigated  nuisances,  are,  in  some  places, 
of  decided  use.  The  utility  of  molds,  however,  has  little 
to  do  with  household  products,  being  confined  chiefly  to 
the  production  of  certain  types  of  cheeses.  The  flavor 
of  Roquefort  cheese,  for  example,  is  due  chiefly,  if  not 
wholly,  to  the  growth  of  certain  types  of  molds  within 
the  cheese.  These  illustrations  will  serve  to  show  that 
microorganisms,  even  in  the  household,  must  occasionally 
be  looked  upon  as  friends  rather  than  enemies. 

3.    MICROORGANISMS  AND  DISEASE 

Certain  species  of  microorganisms  are  harmful  to 
human  health  and  are  the  cause  of  contagious  diseases. 
They  are  generally  known  as  disease  germs  or  pathogenic 
bacteria.  Fortunately  they  are  few  in  number.  While 
large  numbers  of  species  of  microorganisms  may  be 
troublesome  in  the  household  because  of  their  action 
upon  our  foods,  very  few  species,  comparatively,  are  able 
to  do  harm  in  the  human  body  or  to  produce  disease  if 
they  should  find  entrance.  The  great  majority  of  species 


MICROORGANISMS   AND   DISEASE  7 

are,  then,  harmless  to  human  health,  but  a  small  number 
are  capable  of  producing  disease,  and  for  this  reason  are 
of  especial  interest. 

The  study  of  the  causes  and  cure  of  disease  belongs 
primarily  to  the  physician  and  not  to  the  housewife.  The 
housewife  must,  it  is  true,  occasionally  act  as  the  nurse  of 
persons  suffering  from  contagious  diseases,  and  will  then 
be  interested  in  the  treatment  of  the  patient  and  the  cure 
of  the  disease.  But  even  here  the  question  of  cure  must 
be  left  to  the  medical  profession,  while  as  nurse  she  should 
simply  follow  the  directions  given.  Yet  one  phase  of  the 
matter  is  almost  solely  hers,  for  to  her  must  be  left  the 
task  of  preventing  the  distribution  of  contagious  diseases. 
Many  of  the  diseases  produced  by  microorganisms  are 
distinctly  contagious  and,  unless  the  patient  and  the  other 
members  of  the  home  are  properly  guarded,  a  disease 
is  likely  to  be  carried  through  a  household  from  one 
person  to  another.  To  prevent  the  distribution  of  such 
contagious  diseases  is  the  duty  of  those  who  care  for 
the  home. 

The  problem  of  preventing  the  distribution  of  various 
diseases  is  a  bacteriological  one,  for,  inasmuch  as  bacteria 
are  usually  the  cause  of  the  disease,  the  prevention  of 
contagion  is  the  prevention  of  the  distribution  of  bac- 
teria. In  every  home  such  problems  are  more  or  less  com- 
mon. They  concern  the  members  of  the  home  far  more 
materially  than  they  do  the  physician.  Every  household 
will  occasionally  have  experience  with  contagious  diseases, 
and  the  question  of  preventing  their  distribution  from  a 
patient  to  a  healthy  individual  is  sure  to  arise.  The  house- 
wife who  cares  for  the  home  year  after  year  will  have 


8         BACTERIA,  YEASTS,  AND  MOLDS 

many  experiences  where  a  knowledge  of  distribution  of 
diseases  is  of  even  more  importance  to  her  than  to  the 
physician  himself.  The  physician  is  directly  concerned  in 
the  cure  and  only  indirectly  in  the  prevention  of  contagion  ; 
the  housewife  must  always  have  upon  her  shoulders  the 
duty  of  keeping  her  family  in  health,  and  when  an  instance 
of  contagious  disease  appears  she  must  try  to  protect  the 
rest  of  the  household.  For  these  reasons  it  follows  that 
a  knowledge  of  disease  germs  is  of  more  vital  significance 
to  one  who  cares  for  the  home  than  it  is  to  the  physician, 
who  is  only  concerned  in  curing  the  disease.  The  physi- 
cian or  the  Board  of  Health  may  give  suggestions  and 
directions,  but  the  successful  application  of  these  direc- 
tions depends  upon  the  intelligence  of  the  home  keeper. 

This  brief  outline  of  the  relation  of  bacteria  to  various 
household  problems  is  sufficient  to  show  why  a  knowledge 
of  microorganisms  should  be  a  part  of  the  equipment  of 
any  one  who  is  to  conduct  the  affairs  of  a  well-regulated 
household.  For  the  development  and  preparation  of  some 
foods,  for  the  preservation  of  all  foods,  and  for  the  pro- 
tection of  the  health  of  those  under  her  care,  the  head  of 
a  modern  well-equipped  home  needs  to  understand  bac- 
teria and  kindred  organisms.  A  knowledge  of  molds, 
yeasts,  and  bacteria  has  become  a  vital  if  not  a  necessary 
part  of  training  in  domestic  economy. 


DIFFERENT  CLASSES  OF  .MICROORGANISMS 

The  microorganisms  with  which  we  are  concerned  all 
have  one  common  characteristic  :  they  are  what  botanists 
call  colorless  plants.  This  does  not  mean  that  they  are 


CLASSIFICATION   OF   MICROORGANISMS  9 

absolutely  without  color,  for  they  may  be  bluish,  reddish, 
gray,  or  white,  or,  indeed,  they  may  show  other  colors ; 
but  it  means  that  they  do  not  have  the  green  color  char- 
acteristic of  the  majority  of  plants  in  nature.  The  absence 
of  this  green  coloring  makes  them  unable  to  live  upon  the 
food  in  the  soil,  and  forces  them  to  live  upon  a  kind  of 
food  different  from  that  of  ordinary  plants.  Ordinary 
green  plants  can  live  upon  minerals  which  they  obtain 
from  the  soil,  and  upon  gases  which  they  obtain  from  the 
air,  but  the  colorless  plants  cannot  use  such  materials 
at  all.  They  need  a  more  complex  type  of  food. 

The  materials  in  nature  are  frequently  divided  into 
mineral  and  organic  substances.  Mineral,  or  inorganic,  sub- 
stances are  such'  materials  as  rocks,  sand,  earth,  etc. 
Organic  substances  (wood,  bones,  fruit,  muscle,  etc.) 
are  those  which  have  been  produced  by  animals  or  by 
plants,  i.e.  by  organisms.  Evidently  the  foods  we  eat  — 
meats,  fruits,  vegetables,  etc.  —  are  organic,  since  they  all 
come  from  plants  or  animals.  The  colorless  plants  —  the 
Fungi  —  are,  like  animals,  obliged  to  have  organic  sub- 
stances for  foods,  and  therefore  feed  upon  materials  essen- 
tially similar  to  those  which  form  the  food  of  animals,  i.e. 
meats,  fats,  sugars,  etc.  Since  the  colorless  plants  and 
the  animals  are  in  need  of  the  same  kinds  of  food  they 
become  rivals  in  nature.  The  green  plants,  on  the  other 
hand,  living  upon  totally  different  foods,  are  in  no  sense 
the  rivals  of  animals,  but  their  allies.  It  is  this  fact,  their 
living  upon  organic  foods,  that  makes  the  colorless  plants 
of  so  much  importance  for  good  or  ill,  and  explains  their 
close  relation  to  the  problems  of  the  household  with  which 
we  are  concerned. 


10        BACTERIA,  YEASTS,  AND  MOLDS 

Botanists  class  all  colorless  plants  under  one  general 
group,  which  they  call  Fungi.  Under  this  group  is  a  large 
variety  of  plants  which  show  wide  differences  of  structure 
in  size  and  general  appearance.  But  inasmuch  as  they 
all  agree  in  lacking  green  coloring  material,  they  are,  at 
least  from  the  standpoint  of  their  relations  in  nature,  prop- 
erly placed  in  one  general  class.  The  group  of  fungi  as 
recognized  by  botanists  is  subdivided  into,  a  number  of 
divisions.  A  method  of  dividing  them,  convenient  for 
our  purposes,  is  as  follows. 

FUNGI 

Higher  Fungi.  This  includes  the  forms  of  large  size, 
known  generally  as  mushrooms,  toadstools,  wood  fungi, 
rusts,  smuts,  etc.  With  these  plants  we  are  not  particu- 
larly concerned  in  the  household. 

Molds.  Fungi  of  considerable  size,  easily  visible  to  the 
naked  eye,  composed  of  threads. 

Yeasts.  Microscopic  plants  which  multiply  by  a  pro- 
cess called  budding,  composed  of  oval  bodies. 

Bacteria.  Still  smaller  plants  that  multiply  by  a  pro- 
cess called  fission,  composed  of  spherical,  rod-shaped,  or 
spiral  bodies. 

Trrb  classification  is  not  scientifically  accurate.  The 
higher  fungi  include  a  large  number  of  different  types 
classed  by  botanists  into  many  subdivisions.  But  since 
they  are  not  concerned  in  household  problems  we  may 
most  conveniently  group  them  together  and  consider  them 
no  further. 

The  group  of  molds  also  is  not  a  proper  scientific  divi- 
sion, since  under  this  head  are  included  several  different 


CLASSIFICATION   OF   MICROORGANISMS  n 

kinds  of  plants  which  botanists  agree  must  be  separated 
into  several  divisions.  Some  of  the  so-called  molds  really 
belong  to  the  higher  fungi.  But  though  the  term  "mold" 
is  not  a  good  scientific  one,  practically  it  is  very  useful. 
It  is  a  common  English  word,  quite  generally  understood, 
and  always  refers  to  a  variety  of  plants  characterized 
by  a  general  appearance  so  well  known  as  to  be  easily 
recognized  by  persons  who  are  entirely  unfamiliar  with 
scientific  botany.  Although  admitting  that  the  molds  do 
not  represent  any  real  scientific  division  of  fungi,  we  may 
use  the  term  as  referring  to  colorless  plants  which  every 
one  recognizes  but  which  cannot  be  scientifically  defined. 

The  other  two  groups,  yeasts  and  bacteria,  are  proper 
scientific  divisions. 

In  our  study  of  household  problems  we  are  concerned 
only  with  molds,  yeasts,  and  bacteria. 


SECTION  I --MOLDS 

CHAPTER  II 
THE  GENERAL  NATURE  OF  MOLDS 

As  intimated  in  the  last  page,  the  group  of  molds  does 
not  form  a  scientific  division.  Among  the  plants  grouped 
under  this  popular  name  are  included  representatives  of 
several  different  groups  of  fungi.  The  general  character 
of  molds  is  a  dense  mass  of  fine  white  threads.  But  some 
of  the  higher  fungi  related  to  the  toadstools  produce  a 
white  threadlike  mass,  and  if  we  find  this  growing  in 
abundance  upon  the  surface  of  wood  we  commonly  call 
it  a  mold.  Other  so-called  molds  belong  to  the  different 
subdivisions  related  to  cup  fungi,  Ascomycetes,  while  still 
others  belong  to  an  order  of  fungi  which  includes  parasitic 
plants  like  rusts  and  smuts,  and  are  called  JEcidiomycetes. 
We  must  not,  therefore,  look'  upon  molds  as  a  division 
which  would  be  recognized  by  any  botanist.  For  house- 
hold purposes,  however,  no  term  can  take  the  place  of  this 
one,  so  universally  known  and  so  thoroughly  understood. 
In  our  studies,  therefore,  we  shall  group  together  as  molds 
all  types  of  fungi  which  produce  white  felted  threads,  which 
have  the  power  of  growing  in  or  upon  food  materials,  and 
which  give  rise  to  the  well-known  appearance  that  char- 
acterizes the  plants  going  under  this  common  name.  Most 
of  them  are  closely  related  to  each  other. 

12 


THE  GENERAL  NATURE  OF  MOLDS 


The  general  appearance  of  molds  is  well  known  to  every 
one.  At  first  they  are  soft,  fluffy  masses,  usually  white, 
though  later  they  may  become  blue,  green,  brown,  black, 
or  red.  They  grow  upon  all  sorts  of  material  and,  under 
some  conditions,  with 
very  great  rapidity. 
A  typical  mold  as  it 
appears  to  the  naked 
eye  is  shown  in  Fig.  2. 
The  molds  which  are 
liable  to  appear  on  the 
foods  in  the  household 
are  by  no  means  always 
alike,thoughthe  house- 
keeper rarely  recog- 
nizes any  difference 
between  them.  They 
differ  in  many  respects, 
—  in  the  fineness  of 
the  threads  of  which 
they  are  made,  in  the 
rapidity  of  their 
growth,  in  the  mate- 
rials upon  which  they 
grow,  and  more  partic- 
ularly in  color  ;  for  while  most  are  white  at  first,  they  show 
many  other  colors  later.  The  most  common  of  the  house- 
hold molds  is  one  which  at  the  time  of  fruiting  becomes 
a  bluish-green  color,  and  hence  is  called  the  "blue  mold," 
Penicillium  glaucum  (see  Figs.  I  and  5).  This  species 
is  common  upon  bread  and  cheese,  but  it  will  grow  upon 


FIG.  i.  Two  colonies  of  common  mold, 
Penicillium,  as  shown  under  the  micro- 
scope on  a  black  background. 


14  BACTERIA,   YEASTS,  AND   MOLDS 


FIG.  2.     A  piece  of  bread  upon  which  one  of  the  common  molds 
(Mucor)  is  growing. 


FIG.  3.     A  common  mold,  Mucor,  growing  on  a  bit  of  banana. 


THE  GENERAL  NATURE  OF  MOLDS 


leather,  as  well  as  upon  a  host  of  other  materials.  We 
frequently  find  upon  other  foods,  especially  fruits,  two  or 
three  kinds  of  brown  molds,  and  some  that  even  when 
fruiting  remain  pure  white.  Some,  again,  become  pretty 


FIG.  4.  The  sprouting  of  the 
spores  of  Penicillium.  At  b 
there  is  a  cluster  of  seven 
spores  sprouting  to  form  a 
colony. 

nearly  black,  while  still 
others  grow  red  or  pink. 
One  of  the  very  common 
forms  consists  of  a  rather 
coarse  mass  of  threads, 
upon  which  develop 
numerous  rounded  black 
balls  about  the  size  of  a 

period,  while  another  consists  of  delicate  threads  with 
clusters  of  white  spores  looking  like  snowballs.  Each  of 
these  different  colors  indicates  a  different  species  of  mold. 
There  are  scores  of  species  known  to  botanists,  but  it  is 
quite  unnecessary  for  the  housekeeper  to  attempt  to  dis- 
tinguish them.  Pieces  of  moldy  lemon,  banana,  apple,  and 
bread  will  be  quite  sure  to  show  different  species  of  molds. 


FIG.  6.  A  cluster 
of  spores  of  an 
older  colony. 

FIG.  5.  The  growth  from  two  spores 
two  days  later  than  Fig.  4,  showing 
the  beginning  of  the  formation  of 
spores,  showing  method  of  origin  at 
a,  b,  c. 


16  BACTERIA,   YEASTS,  AND   MOLDS 

STRUCTURE  OF  MOLDS 

It  requires  microscopic  study  to  make  out  the  structure 
of  molds,  but  it  is  important  to  understand  this  structure  in 
order  to  be  able  to  explain  the  conditions  under  which  they 
grow.  If  we  study  a  young  mold  before  it  has  begun  to 
produce  its  fruit,  it  is  found  to  consist  of  a  long,  highly 
branching  thread  (Fig.  5).  When  it  begins  to  grow  all 
that  can  be  seen  is  this  tangled  mass  of  delicate  threads. 
The  threads  are  so  minute,  as  a  rule,  that  the  individual 
fibers  are  only  just  large  enough  to  be  seen  by  the  naked 
eye,  and  in  many  cases  they  are  too  small  to  be  seen 
except  with  a  lens.  The  thread  of  the  blue  mold  is  too 
small  to  be  seen  without  a  microscope.  The  threads  are 
practically  always  of  a  whitish  color,  nearly  transparent 
when  examined  under  the  microscope,  and  appear  as 
shown  in  the  several  figures.  In  some  species  of  molds 
they  grow  into  a  very  dense,  felty,  rather  tough  mass. 
In  other  species  they  form  a  loose  mass  of  coarser  fibers 
(Fig.  2). 

An  important  point  to  be  remembered  is  that  these 
threads,  by  their  growth,  can  penetrate  into  the  depths  of 
the  material  upon  which  they  are  growing.  If  they  are 
upon  the  surface  of  bread,  the  fine  fibers  push  their  way 
down  into  the  substance  of  the  bread.  If  they  grow  upon 
cheese,  the  threads  force  their  way  into  the  body  of  the 
cheese.  When  growing  upon  any  soft  food  material,  the 
mold  threads,  though  visible  only  on  the  surface,  really 
extend  into  the  substance  for  a  considerable  distance, 
although  they  are  so  small  and  transparent  that  we  cannot 
follow  them.  Of  course  the  readiness  with  which  a  mold 


THE  GENERAL  NATURE  OF  MOLDS      17 

can  grow  through  food  material  will  depend  upon  the  tough- 
ness or  firmness  of  the  material.  Upon  damp  leather  the 
thread  is  not  capable  of  growing  underneath  the  surface 
so  readily  as  it  can  upon  bread.  This  thread  is  known  to 
botanists  by  the  term  mycelium,  and  by  this  term  we  shall 
hereafter  refer  to  it.  The  young  mold  is  a  white,  loose 
mass  of  mycelium,  but  as  it  grows  older  it  becomes  denser 
by  continued  branching  of  the  thread. 

Fruit.  After  a  while  (usually  two  or  three  days'  growth) 
the  surface  of  the  mold  begins  to  show  some  color,  — 
either  blue,  brown,  red,  or  some  other  color.  The  appear- 
ance of  the  color  on  the  surface  indicates  that  the  plant 
is  fruiting,  i.e.  producing  spores  or  reproductive  bodies. 
The  spores  of  different  species  of  mold  are  produced  in 
quite  different  ways,  and  botanists  classify  molds  by  their 
methods  of  forming  fruit.  It  will  not  be  necessary  for  us 
to  consider  more  than  one  or  two  of  them. 

In  the  common  blue  mold  the  spores  are  produced  as 
follows.  After  the  mycelium  has  grown  for  some  time 
there  arise  from  its  surface  tiny  threads  growing  vertically 
into  the  air.  These  threads,  after  extending  for  a  very 
short  distance,  divide  into  little  branches  (as  shown  in  * 
Fig.  5,  c),  several  branches  arising  from  a  single  stem. 
After  these  branches  have  grown  for  a  short  distance 
they  begin  to  be  divided  by  slight  constrictions,  like  rings, 
around  them,  so  that  each  one  of  them  looks  like  a  string 
of  beads  (Fig.  5,  c).  These  rings  cut  deeper  and  deeper 
into  the  branch  until  finally  it  is  broken  up  into  a  string 
of  a  dozen  or  more  small  round  balls  (Fig.  6).  These 
little  balls  (Fig.  6)  are  the  spores.  When  seen  under  the 
microscope  they  appear  quite  transparent,  but  when  a 


18        BACTERIA,  YEASTS,  AND  MOLDS 

considerable  number  of  them  are  seen  together  they  have 
a  bluish  tinge.  The  spore-bearing  branches  spring  up  in 
thousands  all  over  the  mold,  and  after  a  few  days  its  sur- 
face is  covered  with  a  mass  of  thousands  of  spores,  giving 
to  the  mold  first  a  slightly  blue  color  and  later  a  darker 

blue,  until  the  entire  sur- 
face finally  becomes   cov- 
ered with  the  well-known 
shade   spoken   of   as   blue 
mold.     These 
spores    are    ex- 
tremely  light, 
are   very   easily 
blown   by  the 
winds  and  readi- 
ly float  in  the  air. 
Every  breath  of 

FIG.  7.     A  colony  of  Mucor,  showing  the  mycelium    ,  -    •  i   • 

,  .  .        /•!/••  air  striKinsf  a 

and  the  sporangium  of  the  fruit  capsules.     At  a 

is  a  large  sporangium  filled  with  spores.  mass    of     molds 

in  full  fruit  will 

detach  some  of  these  minute  spores  and  blow  them  away. 
The  species  of  different  molds  can  easily  be  distinguished 
by  their  different  modes  of  forming  spores.  A  mold  com- 
mon on  fruit  and  bread,  called  .Mucor  (Fig.  2),  produces 
its  spores  inside  of  little  sacs  borne  on  long  stalks.  The 
mycelium  in  this  mold  is  coarse  and  the  threads  are  easily 
visible,  making  a  loose  mass  of  delicate  fibers,  and  some- 
times forming  upon  bread  a  fluffy  growth  an  inch  thick 
(Fig.  2).  When  ready  to  fruit,  threads  grow  vertically 
into  the  air  and  the  end  of  each  thread  soon  swelh  into  a 
small  rounded  knob.  This  knob  continues  to  grow  until 


FRUITING   OF  MOLDS 


it  becomes  a  ball  of  considerable  size,  at  first  white,  but 

finally  black,  and  large  enough  to  be  seen  with  the  naked 

eye  (Fig.  7).     Inside  of  this  ball  the  living  substance  of 

the  plant  soon  breaks  up  into  hundreds  of  minute  bodies 

(Fig.   7).     These    are    the    spores,   and    after   they  have 

become  formed  the  sacs  which  hold  them  (sporangia}  burst 

and  .the  little  spores  are  thrown  out  to  be  blown  about 

by  the  wind. 

These  molds 

are  at  first  soft 

and  white,  but 

later  black  from 

the  abundance 

of  these  spore 

sacs. 

Another  very 
common  sort  of 
mold  fruits  still 
differently^- 
pergillus).  A 

fine    threadlike  FlG- 8.     A  colony  of  Aspergillus,  showing  mycelium 

,  .  and   spore   clusters.     The   lower   figures    show   in 

nyC                    1S  detail  the  method  of  spore  formation, 
produced,  as  in 

the  other  cases,  and  from  it  grow  the  fruiting  branches. 
At  the  end  of  each  fruiting  branch  grows  a  little  round 
ball,  from  all  sides  of  which  project  many  little  knobs 
(Fig.  8,  a).  These  knobs  lengthen  a  little,  but  soon  break 
up  into  round  spores  very  much  like  the  branches  of  blue 
mold  (Fig.  8,  a'-e).  The  result  is  that,  since  they  pro- 
trude in. all  directions,  there  appears  on  the  end  of  each 
fruiting  branch  a  little  rounded  mass,  looking  very  much 


20 


BACTERIA,  YEASTS,  AND   MOLDS 


like  a  corn  ball  (Fig.  8,  d),  —  a  resemblance  which  is  very 
striking  in  some  species  when  the  spores  are  white.  This 
species  of  mold,  even  after  producing  its  fruit,  remains 
white ;  but  a  careful  examination  shows  it  to  be  covered 
all  over  with  minute  white  balls  just  big  enough  to  be 
seen  by  the  naked  eye,  but  looking  very  beautiful  under 

the  microscope 
(Fig.  9).  Each 
ball  is  a  mass  of 
scores  of  spores. 
Some  molds  of  this 
last  type  produce 
brown  spores  in- 
stead of  white. 

Of  the  scores  of 
species  of  molds 
each  has  its  own 
method  of  produ- 
cing spores.  Each 
is  at  first  a  white, 
threadlike  myce- 
lium, but  each  in 
time  shows  spots 
of  color.  When  the  color  begins  to  appear  it  commonly 
means  that  the  mold  is  producing  spores.  The  spores 
are  nearly  always  so  small  and  light  as  to  be  blown  easily 
by  the  wind,  and  in  this  way  they  are  carried  to  and  fro. 
The  air  in  any  household  is  almost  sure  to  be  filled  with 
them  in  greater  or  less  abundance,  as  can  easily  be  proved 
by  simple  experiment.  Figs.  14-17  show  a  variety  of  com- 
mon molds,  with  their  methods  of  forming  spores. 


FIG.  9.    A  colony  of  Aspergillus  as  shown  under 
the  microscope  on  a  black  background. 


FRUITING  OF    MOLDS 


21 


FIG.  10.     Mucor,  a 
common  mold. 


FIG.  ii.  Antenaria,  a  com- 
mon mold  found  upon  apples. 
Mycelium  shown  at  a,  and  en- 
larged fruiting  bodies  at  b. 


FIG.  13.  Fruiting  bodies 
of  a  mold  found  upon 
apple  scab,  Cephalo- 
thecium. 


FIG.  12.     Fruiting  bodies  of  another 
species  of  Antenaria, 


FIG.  14.  Stysanus,  a 
mold,  a,  mycelium  ; 
branch. 


common 
,  fruiting 


FIG.  15.    A  common  household  mold. 


22 


BACTERIA,  YEASTS,  AND    MOLDS 


Germination  of  Spores.  The  function  of  these  spores 
is  to  reproduce  the  plant.  If  one  of  them  lights  upon  a 
proper  material  having  sufficient  warmth,  moisture,  and 
nourishment  for  its  life,  it  soon  germinates  and  sends  out 
from  itself  a  little  thread  (Fig.  5,  a).  This  thread  feeds 
upon  the  material  on  which  it  is  growing,  and  continues  to 

extend  and  branch  until  within 
«   -o "Spores 

a  tew  hours  a  new  mycelium  is 

produced,  thrusting  its  way  into 


Spores 


FIGS.  1 6  and  17.     Two  species  of  molds,  Monilia,  common  in  cheese. 

the  food  substance  and  developing  into  a  typical  mold. 
After  a  day  or  two  the  spores  are  again  produced  (Fig.  5), 
and  the  process  is  repeated.  The  air  is  almost  always  so 
well  filled  with  spores  of  molds  that  it  is  quite  impossible 
to  leave  any  food  product  exposed  for  any  length  of  time 
without  a  number  of  these  living  spores  falling  upon  it. 
If  a  piece  of  moist  bread,  for  example,  is  exposed  to  the 
air  for  an  hour  or  so  in  an  ordinary  room,  and  is  then  cov- 
ered with  a  bell  glass  in  such  a  way  as  to  keep  it  moist,  it 
will,  in  the  course  of  a  day  or  two,  become  covered  with 
molds  which  have  come  from  the  sprouting  of  spores  that 


FRUITING   OF   MOLDS 


PLATE  I 


PLATE  II 


FIG.  1 8.  Plates  exposed  to  the  air  before  and  after 
sweeping,  showing  the  abundance  of  mold  spores 
in  the  air.  The  upper  plate  was  exposed  before 
sweeping,  and  contains  one  mold;  the  lower  after 
sweeping,  and  contains  numerous  molds.  Each 
was  exposed  for  one  minute. 


24  BACTERIA,   YEASTS,  AND    MOLDS 

fall  upon  it.  These  spores  —  including  species  already 
described,  as  well  as  a  variety  of  others  —  are  almost  sure 
to  be  floating  in  the  air,  and  one  of  the  valuable  practical 
lessons  for  the  housewife  to  learn  is  that  the  ordinary  air 
of  her  house  is  filled  with  mold  spores  which  are  sure  to 
get  upon  any  food  material  that  is  left  exposed. 

The  mold  spores,  although  very  light,  are  slightly 
heavier  than  the  air,  and  after  floating  awhile  they  sink 
to  the  floor,  if  the  air  is  quiet,  where  they  remain  until 
the  air  is  again  disturbed.  Sweeping  stirs  them  up,  and 
so  does  dusting.  Fig.  18  represents  two  plates  filled  with 
a  jelly  upon  which  molds  will  readily  grow.  .  Plate  I  was 
opened  to  the  air  for  one  minute  in  an  ordinary  room  and 
then  closed.  The  room  was  then  swept  and  Plate  II  was 
exposed  to  the  air  for  the  same  length  of  time.  Both 
were  then  set  aside  until  the  spores  germinated,  when  the 
photographs  were  made.  The  plate  exposed  to  ordinary 
air  shows  only  one  mold,  while  that  exposed  after  the  room 
was  swept  contained  large  numbers.  Dusting  a  room  pro- 
duces similar  results.  Even  walking  through  a  room,  espe- 
cially with  long  dresses  that  sweep  the  floor,  will  stir  up 
mold  spores.  The  practical  conclusions  are  thus  taught 
that  wiping  up  dust  with  a  damp  cloth  is  far  better  than 
dusting  ;  that  carpet  sweepers  are  better  than  brooms;  and 
lastly,  that  no  food  should  be  exposed  to  the  air  of  a 
recently  swept  room. 

PROTECTION  OF  FOOD  FROM  MOLDS 

The  fact  that  the  molding  of  food  starts  from  spores 
that  drop  upon  it  from  the  air  suggests  protecting  the 
food  by  the  simple  means  of  keeping  the  spores  away  from 


PROTECTION    OF    FOOD  25 

it.  If  we  can  keep  the  spores  away,  no  trouble  of  this 
sort  will  arise.  For  example,  jellies  made  from  the  juice 
of  fruit,  which  the  housewife  puts  up  for  winter  use,  are 
excellent  material  for  mold  growth,  as  many  a  person  has 
discovered  after  the  jellies  have  been  stored  away  for  a 
time.  There  is,  however,  little  difficulty  in  preventing  the 
molding.  In  making  the  jelly  the  material  is  commonly 
heated  sufficiently  to  kill  the  spores  present,  and  if  it 
is  afterwards  properly  covered  it  will  keep  well  enough. 
After  the  jelly  has  been  poured  into  the  jelly  tumblers 
and  has  become  somewhat  hardened,  the  surface  should 
be  moistened  with  some  alcoholic  solution,  like  brandy,  or 
even  pure  alcohol.  Then  a  piece  of  clean  white  paper  the 
size  of  the  tumbler  should  be  placed  upon  the  surface  of 
the  jelly.  After  this  the  tumbler  should  be  covered  with 
a  piece  of  paper  tightly  glued  over  its  edges ;  or  tumblers 
with  special  covers  may  be  used  instead  of  ordinary  tum- 
blers covered  with  paper.  The  alcohol  aids  in  destroying 
the  spores  that  may  have  chanced  to  light  on  the  surface 
of  the  jelly,  and  the  paper,  if  properly  fastened,  will  pre- 
vent the  entrance  of  more.  This  device  is  not  sufficient 
to  exclude  bacteria,  and  if  the  jelly  were  liable  to  decay, 
the  simple  paper  covers  would  not  protect  it  from  bac- 
terial action.  But  the  method  is  sufficient  to  prevent 
the  growth  of  molds  in  a  majority  of  cases.  Molds  fre- 
quently grow  upon  the  top  of  the  papers  in  such  jelly 
tumblers,  but  they  do  no  hurt  to  the  contents  below. 

Other  devices  for  closing  the  tumblers  are  also  used. 
Sometimes  a  little  white  of  an  egg  is  used  instead  of  alco- 
hol. Instead  of  using  paper,  a  little  melted  paraffin  may 
be  poured  upon  the  surface  of  the  jelly,  thus  sealing  it 


26  BACTERIA,   YEASTS,  AND   MOLDS 

effectually.  The  paraffin  should  be  melted  in  some  dish, 
like  a  cup,  at  the  lowest  temperature  at  which  it  will  melt, 
about  140°.  The  surface  of  the  jelly  may  then  be  covered 
with  a  thin  layer,  which  will  quickly  harden. 

These  methods  of  protecting  jelly  are  not  sure,  and 
even  after  sealing  it  is  necessary  to  keep  the  jelly  in  a 
dry  place  to  insure  its  keeping  properly.  Spores  may  be 
left  under  the  paraffin,  and  it  is  difficult  or  impossible  to 
seal  so  that  no  mold  spore  can  subsequently  enter.  Jel- 
lies should  therefore  be  stored  in  dry  closets  to  keep  them 
from  spoiling.  If  it  should  happen  that  no  dry  closet  is 
convenient,  the  air  in  a  damp  closet  may  be  partly  dried  by 
keeping  unslaked  lime  in  bowls  on  shelves  near  the  jelly. 
These  will  absorb  the  moisture  and  aid  in  checking  the 
molding.  The  lime  should  be  renewed  from  time  to  time. 

Canned  goods  will  also  sometimes  mold  when  the 
process  of  canning  has  not  been  thorough.  This  will 
however  be  considered  later.  We  must  notice  here,  how- 
ever, that  when  cans  of  fruit  are  opened  and  exposed  to 
the  air,  mold  spores  are  very  likely  to  drop  into  them,  and 
if  they  are  then  shut  up  again  the  contents  of  the  can  are 
almost  sure  to  show  a  fine  crop  of  molds  in  a  few  days. 
It  is  almost  impossible  to  open  a  can  of  fruit,  take  out  a 
part  of  it,  and  close  again,  without  allowing  mold  spores 
to  drop  into  it  from  the  air.  This  must,  of  course,  be 
guarded  against,  and  if  the  whole  contents  of  the  can  can- 
not be  used  at  once,  the  part  that  remains  should  be  boiled 
and  once  more  closed,  as  in  the  original  canning.  By  such 
heating  the  spores  that  may  have  dropped  in  while  the 
can  was  opened  are  destroyed,  and  it  may  be  closed  and 
set  away  safely. 


MATERIAL   LIABLE   TO   MOLD  27 

MATERIAL  WHICH  is  LIABLE  TO  MOLD 

Since  molds  are  fungi,  they  require  to  be  fed  with  organic 
food.  Hence  they  are  unable  to  live,  as  green  plants  can, 
in  purely  mineral  soil.  Indeed,  they  do  not  grow  readily 
anywhere  except  upon  rich  food,  and  they  grow  best  when 
feeding  upon  the  same  kind  of  foods  that  animals  require. 
Whatever  contains  organic  material  will  support  them. 
They  feed  readily  upon  bread,  cheese,  or  meat,  and  they 
can  also  support  themselves  upon  leather  or  upon  woolen 
or  cotton  cloth.  Some  molds  grow  easily  upon  damp 
wood ;  but  although  thus  capable  of  living  upon  almost 
anything  except  mineral  matter,  they  grow  much  more 
readily  on  some  materials  than  on  others. 

Of  common  foods,  cheese  is  probably  the  one  that 
molds  most  readily,  partly  because  it  is  always  more  or 
less  moist,  and  partly  because  it  is  quite  sure  to  be  inoc- 
ulated with  mold  spores.  Wheat  flour,  or  any  material 
made  from  it,  like  bread  or  cake,  is  sure  to  mold  if  kept 
sufficiently  moist  and  warm.  The  molding  of  the  flour  in 
the  flour  barrel  is  occasionally  noticed,  and  the  molding  of 
bread  is  a  common  occurrence.  All  other  forms  of  flour 
and  meal,  as  well  as  articles  made  from  them,  mold  readily 
enough.  Even  pickles  will  occasionally  mold ;  for  the 
intense  acid  of  the  vinegar,  while  it  quite  prevents  the 
action  of  the  common  putrefactive  organisms,  does  not 
necessarily  stop  the  growth  of  molds.  In  short,  almost 
any  of  the  foods  which  are  found  in  the  pantry  may,  under 
certain  conditions,  show  mold  growth  upon  their  surfaces. 

Molding  is  not  confined  to  food  in  the  pantry,  for  other 
substances  which  contain  organic  material  can  furnish 


28        BACTERIA,  YEASTS,  AND  MOLDS 

proper  sustenance  for  mold  growth.  Leather,  like  that 
of  old  shoes,  if  kept  in  a  warm,  moist  atmosphere,  becomes 
covered  with  mildew.  The  same  is  true  of  carpets  and  of 
woolen  or  cotton  cloth.  Such  material  does  not  furnish 
a  very  luxuriant  growth,  the  effect  being  commonly  called 
mildew  instead  of  molding.  At  first  sight  there  seems 
little  similarity  between  molding  and  mildew,  but  the 
microscope  tells  us  that  mildew  is  really  nothing  more 
than  the  growth  of  certain  species  of  molds  that  have 
not  developed  very  luxuriantly. 

Paper  is  also  liable  to  mold  if  kept  damp,  and  certain 
molds  are  occasionally  found  in  and  upon  books.  Even 
woodwork  will  sometimes  mold,  especially  in  dark,  damp 
cellars.  In  short,  almost  anything  in  the  household  which 
is  of  vegetable  or  animal  nature  may,  under  proper  circum- 
stances, furnish  a  substratum  which  can  develop  a  more  or 
less  luxuriant  crop  of  these  plants. 

RESULTS  OF  MOLD  GROWTH 

The  effect  of  mold  growth  varies  with  the  species  of 
the  mold  and  also  with  the  material  on  which  it  is  grow- 
ing. Sometimes  molds  are  useful,  as  for  example  in  the 
ripening  of  Roquefort  cheeses.  Upon  most  of  our  food 
products,  however,  their  action  is  injurious  in  at  least 
four  directions,  (i)  They  make  the  food  unsightly,  for 
few  people  would  be  willing  to  use  as  food  any  material 
upon  which  a  luxuriant  growth  has  made  its  appearance. 
(2)  They  generally  injure  the  taste  of  the  foods,  for  a 
peculiar  flavor  is  sure  to  be  imparted  to  any  food  product 
where  mold  has  grown,  and  after  the  mold  has  a  luxuriant 
growth  the  flavor  of  the  food  is  so  modified  that  we  are 


RESULTS    OF   MOLD   GROWTH 


29 


usually  not  willing  to  eat  it.  (3)  They  affect  the  odor  of 
food.  Mold  is  always  sure  in  time  to  develop  a  peculiar 
smell  which  we  generally  speak  of  as  ."  musty."  Musti- 
ness,  indeed,  is  commonly  nothing  more  than  the  odor  that 
comes  from  molds.  It  is  due  in  part  to  the  presence  of 
the  microscopic  spores  which  arise  from  the  mold  mass, 
and  which,  breathed  into  the  nostrils,  produce  the  pecul- 
iar effect  upon  the  nose  which  gives  rise  to  the  odor.  It 

is  due  also  in  part  to          ^..^v?:v:v:n^:^---Tr^-. .^... 

gases  which  arise 
from  the  molding 
material  as  the  result 
of  deccmposition.  At 
all  events,  mustiness 
is  always  character- 
istic of  mold  growth, 
and  whenever  any 
material  or  any  room 
smells  musty  we  may 
be  confident  that  it 

contains    growing     FlGt  T9-     A  bit  of  Stilton  cheese.     The  dark 
,  ,          ,T,  ,  parts  are  masses  of  mold  spores. 

molds.     We  may  be 

sure  also  that  any  material  capable  of  molding,  if  left  in 
such  a  musty  room,  will  be  sure  to  show  signs  of  molding 
in  a  short  time.  (4)  In  the  end  the  growth  of  the  molds 
results  in  the  total  ruin  of  the  food,  since  after  a  while 
mold  growth  produces  decomposition,  putrefaction,  and 
decay.  These  later  changes  are  due  to  the  fact  that  the 
molds  are  consuming  the  material  as  their  own  food. 
While  they  use  the  food  for  their  own  purposes  they  are 
producing  chemical  changes  which  result  in  the  production 


30        BACTERIA,  YEASTS,  AND  MOLDS 

of  the  peculiarly  flavored  products  characteristic  of  certain 
forms  of  decay,  rot,  or  putrefaction. 

It  must  not  be  understood,  however,  that  putrefaction 
is  produced  wholly  by  the  action  of  molds,  even  in  the 
materials  on  which  molds  are  visibly  growing  ;  for  another 
class  of  organisms  to  be  considered  later,  the  bacteria,  is 
more  commonly  concerned  in  putrefaction.  But  molds 
contribute  largely  to  the  development  of  putrefaction,  and 
in  the  case  of  some  materials,  as  fruits,  molds  are  prac- 
tically the  sole  cause  of  this  phenomenon. 


MOLDS  UPON  FOOD  NOT  NECESSARILY  UNWHOLESOME 

The  result  of  these  various  changes  is  that  almost  all 
foods  are  soon  spoiled  if  molds  are  allowed  to  grow  upon 

them  for  any  considerable 
time.  They  rapidly  change 
in  flavor,  odor,  and  in  ap- 
pearance, and  eventually 
the  putrefaction  or  decay 
makes  them  utterly  value- 
less. If,  however,  the 
molding  is  checked  quickly 
and  the  food  preserved  from 
A  bit  of  Gorgonzola  further  molding,  or  if  it  is 
consumed  at  once,  there 

is  no  reason  why  the  food  should  not  be  utilized,  for  the 
mold  itself  is  not  particularly  unwholesome.  We  may 
consume  food  that  has  begun  to  mold  without  its  produ- 
cing any  ill  effects  upon  us,  provided  that  the  molding  has 
not  extended  too  far  and  that  we  do  not  eat  a  great  quantity 


FIG.  20. 


USEFUL  MOLDS  31 

of  it.  Indeed,  Stilton  (Fig.  19),  Gorgonzola  (Fig.  20),  and 
Roquefort  cheeses  owe  their  delicious  flavors  to  molds. 
If  a  large  quantity  of  moldy  material  is  taken  at  once,  it 
is  possible  that  a  slight  poisonous  effect  may  be  produced; 
but  this  practically  never  occurs  in  the  consumption  of 
moldy  food.  It  is  well  to  remember,  therefore,  that  molds 
are  not  unhealthful.  It  is  not  always  necessary  to  throw 
away  moldy  food ;  much  of  it  may  be  used.  Moldy 
cheese  is  by  no  means  ruined,  for  the  moldy  surface  may 
be  scraped  off  and  the  center  will  be  found  as  good  as 
ever.  Many  samples  of  preserves  or  jellies  which  are 
beginning  to  mold  may  be  utilized  if  we  simply  stop  the 
growth  of  the  mold  and  preserve  the  food  from  further 
molding.  It  may  be  that  the  mold  has  developed  a  slight 
musty  odor  and  taste,  which  would,  perhaps,  injure  the 
value  of  the  food  from  the  standpoint  of  the  palate,  but 
they  will  not  have  injured  its  ease  of  digestion  or  its  value 
as  a  food. 

It  is,  however,  the  desire  of  the  housewife  to  prevent 
molding  so  far  as  possible,  and  to  check  it  quickly  if  it 
begins,  in  order  that  she  may  thus  preserve  the  valuable 
foods.  To  understand  the  methods  by  which  we  may  best 
prevent  the  growth  of  mold,  or  check  it  if  it  once  begins, 
we  must  next  consider  the  conditions  most  favorable  for 
mold  growth. 


CHAPTER   III 
CONDITIONS    FAVORING    MOLD    GROWTH 

Moisture.  The  factor  of  primary  importance  is  water. 
A  vigorous  growth  of  molds  needs  an  abundance  of  mois- 
ture, and  in  dry  material  they  will  not  grow  at  all.  This 
moisture  may  be  supplied  by  the  air  in  which  the  food  is 
kept,  or  by  the  food  itself. 

1.  Many  materials  which  do  not  contain  in  themselves 
enough  water  to  support  the  development  of  molds  will 
serve  as  a  fine  locality  for  mold  growth,  provided  they  are 
kept  in  a  sufficiently  damp  atmosphere.     If  the  air  of  a 
room  becomes  damp  or  "close,"  as  we  say,  it  is  almost 
certain  that  molds  will  begin  to  grow  upon  any  organic 
substance.     Thus  a  large  variety  of  materials  in  the  house- 
hold, ordinarily  free   from   molding,    may  show   signs  of 
mildew  during  a  damp  season.     The  mustiness  of  a  closed 
room  is  due  to  the  presence  of  molds  and  is  always  an 
indication  of  dampness,  for  dry  rooms  neither  show  signs 
of  mold  nor  do  they  smell  musty. 

2.  Some  materials  contain  within  themselves  sufficient 
water  to  produce  a  vigorous  development  of  molds  quite 
independent  of  the  moisture  present  in  the  air.     Fruits, 
for  example,  are  so  fulV  of  water  that  it  makes  little  differ- 
ence to  them  whether  the  atmosphere  in  which  they  are 
kept  is  dry  or  saturated  with  moisture.     If  the  mold  once 
gets  a  start,  the  fruit  itself  furnishes  all  necessary  water. 

32 


EFFECT   OF    MOISTURE  33 

The  same  might  be  true  of  other  very  moist  food  materials. 
But  while  a  majority  of  food  stuffs  are  liable  to  mold  in 
our  houses,  they  are  commonly  not  moist  enough  to  sup- 
port mold  growth  if  kept  in  a  moderately  dry  atmosphere ; 
and  even  in  the  case  of  fruit  a  moist  atmosphere  is  neces- 
sary to  start  the  growth. 

From  these  facts  it  follows  that  food  capable  of  being 
thoroughly  dried  may  be  protected  absolutely  and  per- 
manently from  molding.  Various  kinds  of  flour  and  meal, 
although  furnishing  excellent  food  for  molds,  will  keep 
indefinitely  while  dry.  This  statement  is  an  absolute  one 
with  no  exception.  It  must,  however,  be  remembered 
that  even  the  driest  of  foods  may  become  moist  in  a 
damp  atmosphere,  and  that  hence  the  driest  material,  if 
exposed  to  a  moist  atmosphere,  may  in  a  short  time  show 
the  growth  of  molds.  Flour  in  a  flour  barrel,  dried  apples 
packed  in  a  box,  and  dried  meat  hung  in  a  shed  may  all 
show  signs  of  mold  in  damp  seasons.  Molds  will  start 
upon  carpets  in  damp  weather,  and  upon  leather  boots  or 
shoes  if  they  are  kept  in  damp  closets  sufficiently  long  for 
the  germination  of  the  mold  spores  that  are  floating  in 
the  air.  Books  in  our  libraries  and  clothes  stored  away 
in  closets  or  drawers  are  not  free  from  molding  in  damp 
weather.  Sometimes  leather  pocketbooks  will  develop  mold 
in  our  pockets,  stimulated  by  the  moisture  and  heat  in  our 
bodies,  and  will  become  covered  with  the  well-known  mil- 
dew. Boxes  of  cotton  cloth  shipped  for  transport  may 
mold  on  their  journey  if  the  weather  is  moist.  In  short, 
in  damp  weather  no  animal  nor  vegetable  material  is  free 
from  the  possibility  of  molding,  and  dryness  is  in  all  cases 
an  efficient  remedy. 


34  BACTERIA,   YEASTS,  AND    MOLDS 

It  is  evident  that  drying  may  be  conveniently  used  for 
preserving  cloth,  leather,  etc.  Thorough  airing  and  drying 
by  exposure  to  sunlight,  followed  by  brushing,  is  the  cure 
for  mildew.  It  is  also  wjell  to  remember  that  soiled  clothes 
mold  much  more  readily  than  clean  clothes,  probably 
because  the  dirt  upon  the  cloth  furnishes  a  little  food  for 
the  molds  which  suits  them  better  than  the  cloth  itself. 
Soiled  clothing,  if  packed  away  and  left  undisturbed  for  a 
time,  is  quite  likely  to  be  injured  by  molding. 

While  moisture  is  necessary  for  mold  growth,  it  is  true, 
on  the  other  hand,  that  too  much  moisture  is  generally 
not  favorable  to  molds.  Very  wet  foods,  like  fresh  meat, 
milk,. etc.,  do  not  commonly  mold,  although  they  readily 
decay  from  the  action  of  bacteria. 

Stagnation  of  the  Air.  Molds  grow  better  in  an  atmos- 
phere where  the  air  is  not  freely  moving,  and  therefore 
are  much  more  vigorous  in  foods  shut  up  in  tight  boxes 
than  in  the  same  foods  when  currents  of  air  are  allowed 
to  flow  over  them.  The  reason  for  this  is  not  wholly 
known.  It  may  be  that  the  agitation  of  the  thread  pro- 
duced by  the  currents  of  air  is  injurious  to  the  growth  of 
molds  ;  but  it  is  more  probable  that  the  air  currents  simply 
tend  to  evaporate  the  moisture  from  the  surface  too  rapidly 
to  allow  the  growth  of  molds.  Certain  it  is  that  a  vigor- 
ous growth  of  mold,  upon  a  bit  of  cheese  for  example, 
will,  when  exposed  to  the  air,  change  from  a  fine,  loose, 
fluffy  mass  to  a  dense,  flat,  matted  layer,  and  will  soon 
almost  cease  to  grow.  Whether  this  is  due  to  evapora- 
tion of  moisture  or  to  some  other  cause  is  a  matter  of  no 
great  practical  importance  in  the  house.  The/act  is  borne 
out  by  long  experience,  that  molds  grow  in  closed  vessels 


EFFECT   OF  AIR   ON    MOLD    GROWTH  35 

much  more  rapidly  than  upon  open  surfaces.  As  a  result 
we  find  that  molding  is  more  likely  to  take  place  in  food 
when  a  number  of  pieces  are  piled  together  in  a  heap,  as, 
for  instance,  several  slices  of  bread  or  a  number  of  pieces 
of  fruit.  Such  a  heap  furnishes  many  little  recesses 
partly  surrounded  by  walls  which  prevent  the  free  pas- 
sage of  air  currents,  and  these  little  nooks  furnish  a 
sheltered  place  for  the  mold  spores  to  germinate.  If  bits 
of  bread  are  spread  out  on  the  shelf  of  a  damp  closet  they 
will  probably  not  mold  at  all,  while  the  same  pieces  would 
mold  if  piled  in  a  heap.  Foods  with  smooth  surfaces  are, 
for  the  same  reason,  not  so  liable  to  mold  as  those  filled 
with  little  cavities,  like  bread. 

On  the  other  hand,  molds  require  some  air,  and  molding 
almost  always  begins  on  the  surface.  Although,  as  we 
have  seen,  the  mold  thread  can  force  its  way  down  into 
the  solid  substance  of  food,  it  always  starts  upon  some  sur- 
face exposed  to  the  air.  To  grow  vigorously,  the  threads 
demand  an  abundance  of  air,  and,  as  a  consequence,  will 
never  grow  in  the  center  of  solid  food  masses,  or  at  least, 
if  they  do,  they  grow  there  very  slowly.  After  starting 
on  the  surface  they  may  grow  for  some  distance  into  solid 
food  substance.  In  the  manufacture  of  Roquefort  cheese 
it  is  desired  that  molds  should  start  at  the  center  of  a  hard 
cheese  mass.  To  bring  this  about  the  growth  is  stimu- 
lated by  piercing  the  cheeses  full  of  holes  by  means  of  long 
needles,  so  that  air  can  penetrate  to  the  center.  Air  is  quite 
necessary  for  the  formation  of  the  spores,  and  the  fruiting 
of  the  mold  practically  always  occurs  upon  the  free  surfaces. 
We  need  not  expect  any  molding  in  the  center  of  a  mass 
of  food  unless  some  signs  of  it  are  visible  externally. 


36        BACTERIA,  YEASTS,  AND  MOLDS 

Darkness.  Molds  will  grow  both  in  light  and  darkness, 
but  on  the  whole  they  grow  somewhat  better  in  darkness 
than  in  light.  Indeed,  the  action  of  direct  sunlight  is 
injurious  to  them,  and  most  species  of  molds  fail  to  grow 
upon  the  surfaces  of  material  exposed  to  sunlight.  As  a 
result  of  this  we  rarely  find  molds  growing  upon  the  free 
surfaces  of  materials  exposed  to  the  sunlight  or  even  to 
bright  light.  This  is  not  universally  true,  but  it  is  the 
common  experience  of  housewives  to  find  that  materials, 
when  shut  up  in  dark  closets,  are  very  much  more  liable 
to  mold  than  when  left  in  a  light  room.  This  is  doubtless 
due,  in  part,  to  the  fact  that  exposure  to  sunlight,  or  even 
to  the  air  of  a  light  room,  evaporates  moisture  rapidly 
and  thus  checks  molding.  But  it  is  not  wholly  due  to 
this,  for  light  itself  appears  to  be  deleterious  to  mold 
growth. 

Temperature.  Molds  require  a  moderately  warm  tem- 
perature for  vigorous  growth.  At  a  temperature  in  the 
vicinity  of  freezing  they  will  not  grow  at  all,  and  at  a  few 
degrees  above  freezing  their  growth  is  very  slight.  Some 
species  of  molds,  however,  grow  readily  enough  at  40°, 
growing  better  at  this  than  at  a  warmer  temperature. 
Hence  it  follows  that  the  temperature  of  an  ice  chest  will 
not  wholly  prevent  molding.  Most  common  molds,  how- 
ever, either  fail  to  grow  at  an  ice-chest  temperature  or 
grow  very  slowly.  As  the  temperature  increases,  how- 
ever, the  growth  becomes  more  vigorous,  and  at  tem- 
peratures varying  from  70°  to  100°  the  growth  of  these 
plants  is  stimulated  to  their  highest  activity.  A  practical 
result  from  these  facts  is  that  any  material  which  can  be 
kept  sufficiently  cool  will  fail  to  show  signs  of  mold,  even 


EFFECT   OF   TEMPERATURE  37 

though  tightly  closed  in  an  atmosphere  saturated  with 
moisture  and  abundantly  sown  with  mold  spores.  In  cold- 
storage  houses,  where  the  temperature  is  below  freezing, 
there  is  no  molding.  If  the  temperature  is  just  above 
freezing,  molding  is  almost  prevented.  The  ice  chest  also, 
though  much  warmer,  very  decidedly  checks  the  tendency 
in  most  foods  to  mold.  Cheese,  for  example,  after  being 
cut,  should  be  kept  in  a  closed  dish,  to  prevent  its  drying 
too  rapidly ;  but  it  molds  rapidly  when  thus  covered.  If 
the  dish  be  placed  in  an  ordinary  refrigerator,  it  will  keep 
a  long  time. 

Killing  by  Heat.  In  considering  the  relation  of  tem- 
perature to  molds  a  fact  of  great  importance  is  that  high 
heat  will  always  destroy  molds  and  their  spores.  A  tem- 
perature considerably  below  boiling,  150°  or  160°,  is  quite 
sufficient  to  destroy  the  mycelium  of  the  molds,  although 
the  spores  may  resist  this  temperature  ;  but  a  temperature 
of  boiling  is  necessary  to  kill  the  spores.  Hence  any 
food  which  has  begun  to  mold,  and  which  is  of  a  character 
to  allow  heating,  may  be  protected  from  the  further  growth 
of  the  mold  by  boiling.  A  temperature  somewhat  below 
boiling  will  check  mold  growth,  though  not  actually  kill- 
ing the  spores.  This  method  of  treatment  will  be  possible 
for  many  preserves,  canned  foods,  or  any  food  that  has 
been  previously  cooked.  It  may  be  applied  to  preserves, 
sauces,  jellies,  mince-meat,  and  even  pickles.  It  would 
not  be  practicable,  however,  with  foods  whose  flavor  is 
destroyed  by  cooking.  Fresh  fruit  which  has  begun  to 
mold  cannot  be  treated  in  this  way  without  destroying 
the  original  fruit  flavor  and  giving  in  its  place  the  taste 
of  fruit  preserves  or  sauce.  It  is  always  necessary  to 


38  BACTERIA,   YEASTS,   AND    MOLDS 

remember  that  after  such  heating  the  food  is  liable  again 
to  receive  more  mold  spores  from  the  air  and  may  there- 
fore later  show  another  growth  of  molds. 

Reaction.  By  reaction  is  meant  the  condition  of  food 
as  to  its  acidity.  Some  foods  are  acid  (lemons,  pickles), 
while  many  may  have  the  opposite  reaction,  called  alkaline. 

The  reaction  of  food  is  a  matter  of  considerable  impor- 
tance in  determining  its  likelihood  to  mold.  It  is  true  that 
both  alkaline  and  acid  foods  may  mold,  but  in  general  acid 
foods  mold  more  readily.  Lemons  are  very  acid,  and  so 
are  ordinary  fruits,  all  of  which  mold  very  quickly.  Molds 
may  even  grow  upon  such  strong  acid  materials  as  pickles. 
Bacteria,  the  second  great  agent  in  producing  decay,  grow 
in  alkaline  but  not  commonly  in  acid  foods.  Hence  it  fol- 
lows that  materials  which  are  most  liable  to  mold  are  not 
likely  to  support  the  growth  of  bacteria,  and  vice  versa. 

PRACTICAL  SUMMARY 

From  these  general  observations  it  will  be  seen  that 
molds  will  grow  best  in  dark,  damp  rooms  or  in  corners 
of  the  rooms  where  there  is  not  free  circulation  of  air ; 
they  will  flourish  in  heaps  of  food  where  many  pieces 
are  massed  together  ;  they  will  grow  vigorously  upon  food 
inclosed  in  jars  or  boxes,  and  they  prefer  darkness  rather 
than  light. 

From  all  these  facts  we  may  reach  practical  sugges- 
tions as  to  the  methods  of  avoiding  the  growth  of  molds, 
(i)  The  most  important  of  all  is  that  food  should,  so  far 
as  possible,  be  kept  tolerably  dry.  If  it  is  of  a  nature  that 
will  stand  drying,  it  may  be  protected  indefinitely  if  once 


PREVENTING    MOLD   GROWTH  39 

dried  and  not  allowed  subsequently  to  become  damp. 
Indeed,  in  a  pantry  or  a  cellar,  molding  commonly  means 
excessive  dampness.  (2)  Foods  are  more  free  from  mold 
if  exposed  as  much  as  practicable  to  light  rather  than  if 
kept  stored  in  dark  boxes.  It  is  of  course  necessary  to 
keep  some  kinds  of  food  in  closed  boxes  in  order  to  pre- 
vent them  from  becoming  too  dry,  but  it  is  useful  to  expose 
such  food  occasionally  to  the  air  and  sunlight  in  order  to 
check  the  development  of  molds  that  otherwise  might 
grow.  (3)  The  growth  of  molds  may  be  almost  com- 
pletely stopped  by  lowering  the  temperature,  and  there- 
fore foods  that  are  particularly  liable  to  mold  may  be 
prevented  from  molding  for  a  long  time  if  kept  in  an 
ice  chest.  The  temperature  of  an  ice  chest  is  not  low 
enough  to  prevent  all  mold  growth,  but  it  is  so  low  that 
some  species  of  molds  do  not  grow  at  all,  while  others 
grow  so  very  slowly  that  even  a  material  like  cheese, 
which  is  quite  sure  to  mold  if  shut  up  in  the  dark  at 
ordinary  temperatures,  may  be  preserved  in  a  dark  ice 
chest  for  many  days  or  even  weeks  without  molding  suffi- 
ciently to  do  it  injury. 


CHAPTER    IV 


THE  DECAY  OF. FRUIT;    USEFUL  MOLDS;    MOLD 
DISEASES 

Of  all  food  materials  commonly  found   in  the  house- 
hold   none    are    so    much    injured    by    molds    as    fruits. 

Most  pears,  plums, 
and  peacJies  decay 
rapidly;  apples, 
oranges,  and  bananas 
keep  so  m  e  what 
longer,  but  it  is  a 
universal  experience 
that  none  of  our 
ordinary  fruits  can 
be  kept  for  any  con- 
siderable length  of 
time  without  de- 

FIG.  21.     An  apple  beginning  to  decay  under       :aymg     (F!g-    2l). 
the  action  of  certain  species  of  molds.  Winter  apples,  with 

their  solid  flesh  and 

their  tough,  smooth  skin,  can  be  kept  for  many  months 
without  rotting,  and  the  thick  skins  of  oranges  and  lemons 
protect  them  a  long  time.  But  thin-skinned  fruits,  like  cher- 
ries or  berries,  can  be  kept  only  a  comparatively  few  days. 
The  decay  of  fruit  is  by  no  means  always  alike,  and  it  is 
produced  by  a  variety  of  causes.  If  one  simply  examines 

40 


THE   DECAY   OF   FRUIT  41 

decaying  apples,  pears,  lemons,  and  bananas,  the  differ- 
ence in  the  character  of  the  decay  is  quite  evident  both 
to  the  eye  and  to  the  smell.  Bitter  rot,  black  rot,  and 
brown  rot  are  three  types  produced  by  three  different 
organisms.  It  is  not  within  the  scope  of  our  study  to 
describe  the  different  kinds  of  decay  which  appear  in  com- 
mon fruit.  The  causes  may  be  numerous,  but  in  the 
majority  of  the  examples  of  decayed  fruit  the  active  agency, 


FIG.  22.     Monilia,  a  common  species  of  mold  causing  fruit  decay. 

at  the  start  at  least,  is  the  growth  of  molds.  In  later 
stages  of  the  decay  bacteria  may  be  concerned,  but  it  is 
always  molds  that  begin  the  process.  There  are  a  num- 
ber of  species  of  molds  intimately  associated  with  the 
decay  of  fruits.  The  common  blue  mold  (Fig.  7)  is  one 
of  the  most  widely  distributed,  but  there  are  several  others 
(Figs.  22,  23,  24). 

METHOD  OF  INFECTION  AND  DISTRIBUTION 

To  understand  the  decay  of  fruit  we  must  first  bear  in 
mind  that  mold  spores  are  constantly  floating  in  the  air, 
and  that  they  may  also  be  carried  easily  upon  the  feet  of 
insects  that  chance  to  light  upon  a  bit  of  spore-bearing 
mold.  By  some  such  agency  mold  spores  are  quite  sure 


BACTERIA,   YEASTS,  AND   MOLDS 


to  find  their  way  to  the  skin  of  any  piece  of  fruit.  But 
after  they  fall  upon  the  fruit  they  will  not  grow  unless 
the  conditions  are  right.  If  the  skin  is  whole  and 
smooth  they  do  not  readily  germinate.  Commonly  they 
start  at  some  small  crack  in  -the  skin  through  which  the 
thread  sprouting  from  the  spore  can  thrust  itself  into 

the  softer  parts  within. 
Hence  whole-skinned  fruits 
are  easier  to  keep  than  those 
with  bruises.  If  the  spores 
find  sufficient  moisture  on  the 
skin,  and  a  convenient  crack, 
they  soon  send  a  tiny  myce- 
lium thread  into  the  fruit. 
This  grows  luxuriantly, 
branching  profusely,  and 
presently  pushes  its  way  in 
every  direction  through  the 
soft  pulp  of  the  fruit.  The 
fruit  begins  to  soften  and 
decay.  The  rotting  is  caused 

fe        fc  {h   Qf   ^   mo]d 

mation   of  spores   at   c   and  the       * 

sprouting  of  spores  at  a  and  b.     mycelium   in   the  flesh,  the 

visible  decaying  spots  being 

simply  the  external  evidence  of  the  mold  growing  within. 
After  a  time  the  mold  begins  to  form  its  spores.  To 
do  this  it  generally  breaks  through  the  skin  so  that  the 
spores  may  be  formed  in  the  air.  These  spores  can  easily 
be  seen  in  a  well-decayed  apple  (Fig.  25).  The  spores 
thus  produced  are  then  scattered  into  the  air  from  the 
broken  skin  of  the  fruit.  They  are  carried  either  by  air 


F,G.23. 


showing  the  for- 


DISTRIBUTION    OF   SPORES 


43 


currents  or  by  insects,  or,  if  the  pieces  of  fruit  are  in 
direct  contact  with  each  other,  as  is  almost  always  the 
case  when  packed,  one  piece  of  fruit  will  directly  infect 
the  next  and  thus  start  a  new  center  of  decay.  In  this 
way  decay  which  begins  with  a  single  piece  of  fruit  is 


FIG.  24.     Another  species  of  Monilia  taken  from  a  decaying  apple, 
showing  formation  of  spores. 

sure  in  a  short  space  of  time  to  extend  to  the  neighbor- 
ing pieces.  From  a  single  decaying  apple,  infection  may 
spread  from  apple  to  apple  until  a  whole  barrel  speedily 
becomes  decayed  and  ruined.  It  is  an  example  of  direct 
contagion. 

A  practical  suggestion  arising  from  these  facts  is  the 
wisdom  of  removing  from  the  vicinity  of  sound  fruits  all 


44 


BACTERIA,  YEASTS,  AND   MOLDS 


that  show  signs  of  decay,  since  decaying  fruit  will  surely 
be  shedding  spores  which  will  infect  the  sound  fruit. 
Such  fruit,  therefore,  should  not  be  allowed  to  remain  in 
a  pantry  with  other  fruit,  nor  in  a  cellar.  Nor  should 
it  be  allowed  to  accumulate  in  heaps  near  the  home,  for 
insects  and  air  currents  are  sure  to  distribute  the  spores. 
The  removal  of  all  decaying  fruit,  or  its  total  destruction, 
therefore,  is  a  necessary  safeguard  to  protect  the  sound 
fruit  that  remains. 

PROTECTION  OF  FRUIT  FROM  DECAY 

There  is  no  thoroughly  successful  remedy  for  the  decay 

of  fruit.  It  is  true  that 
fruit  may  be  preserved 
absolutely  from  such  de- 
cay ;  but  this  can  only 
be  done  by  the  process 
of  canning,  or  by  some 
other  method  of  preserv- 
ing which  involves  oper- 
ations totally  changing 
the  character  of  thefruit. 
These  we  shall  consider 
in  a  later  chapter.  It  is 

FIG.  25.     A  small  bit  of  an  apple  under  a  not    possible    by    any 

microscope,  showing  the  molds  breaking  known  meansto preserve 

through  the  skin  to  produce  spores,  and  fruit     indefinitely    from 
showing  the  mycelium  running  through 

the  substance  of  the  apple.  the  attack  °f  molds  and 

at  the  same  time  to  re- 
tain its  original,  natural, fresh  condition.  Even  the  hardiest 
and  toughest  of  fruits  will,  in  the  course  of  months,  begin  to 


PROTECTING  FRUITS  FROM  DECAY      45 

show  signs  of  decay,  though  some  kinds  may  be  preserved 
much  longer  than  others.  But  although  it  is  not  possible 
to  prevent  absolutely  the  growth  of  molds,  it  is  quite  pos- 
sible to  delay  it  very  materially  if  proper  care  is  taken  of 
the  fruit.  Fruit  which  would  ordinarily  keep  only  a  few 
weeks  may,  if  properly  treated,  be  kept  through  the  winter 
until  the  spring.  Different  fruits  vary  much  in  their  ease 
of  preservation.  Peaches,  cherries,  and  berries  can  hardly 
be  preserved  at  all ;  pears  only  a  little  longer.  Grapes 
can  be  kept  a  few  weeks  or  longer  if  special  care  is  taken. 
Apples,  oranges,  and  lemons  can  be  kept  many  weeks  or 
even  months. 

Moisture.  We  have  seen  that  plenty  of  moisture  is  a 
necessary  condition  of  mold  growth.  But  in  considering 
the  application  of  this  fact  to  the  decaying  of  fruit  we 
must  remember  that  the  interior  of  fresh  fruit  itself  is 
always  moist,  containing,  indeed,  quite  sufficient  water  for 
the  development  of  the  molds,  provided  they  can  once  get 
through  the  skin.  Hence  the  decay  of  fruit  goes  on 
about  equally  well  in  moist  and  in  dry  air,  provided  the 
molds  once  get  a  start,  and  it  cannot  be  prevented  by  keep- 
ing the  fruit  dry. 

But  the  moisture  which  accumulates  upon  the  skin  of 
the  fruit  is  a  most  important  factor  in  its  tendency  to 
decay.  The  mold  spores  are  quite  incapable  of  germinat- 
ing unless  they  are  moistened,  and  any  fruit,  the  skin  of 
which  is  kept  perfectly  dry,  is  very  largely  protected 
from  decay,  because  the  spores  get  no  opportunity  for 
germinating.  If  the  skin  of  the  fruit  can  be  kept  clean 
as  well  as  dry,  the  rotting  may  be  delayed  for  a  very 
long  time. 


46        BACTERIA,  YEASTS,  AND  MOLDS 

This  is  no  easy  matter,  for  there  are  almost  sure  to  be 
some  depressions  in  the  skin,  such  as  cracks  or  dents,  and 
in  these  moisture  is  sure  to  accumulate.  The  depressions 
around  the  stem  or  the  eye  of  an  apple  serve  the  same 
end,  and,  in  damp  air,  water  is  so  likely  to  accumulate 
here  that  molding  starts  readily.  Once  germinated  the 
threads  quickly  force  their  way  into  the  apple  around  the 
stem  and  find  plenty  of  moisture  in  the  flesh  of  the  fruit. 
Hence  any  devices  which  tend  to  keep  the  skin  of  the 
fruit  dry  are  at  the  same  time  devices  for  checking  the 
first  steps  of  decay.  Fruit  whose  skin  is  wiped  frequently 
with  a  dry  cloth  will  keep  better  than  fruit  that  is  not 
thus  wiped.  This  question  of  moisture  explains  also 
why  it  is  that  fruits  begin  to  decay  first  at  points  where 
two  pieces  come  in  contact  with  each  other,  since  here 
there  is  a  much  better  opportunity  for  moisture  to  con- 
dense. We  also  learn  why  fruit  which  has  been  cooled 
to  a  very  low  temperature  —  as  in  cold  storage  —  and 
subsequently  warmed,  may  decay  more  quickly  than  fruit 
which  has  not  been  cooled.  The  cold  skin  of  the  fruit 
taken  from  cold  storage  causes  a  slight  condensation  of 
water,  and  then  when  subsequently  warmed  this  water 
furnishes  a  favorable  starting  point  for  the  germination 
of  mold  spores.  This  explains  also  why  covering  with 
sawdust  or  charcoal  is  of  great  value  in  checking  the 
decay  of  fruit.  If  packed  in  sawdust,  fruit  may  be  pre- 
served a  long  time,  because  the  sawdust  absorbs  moisture 
and  prevents  the  accumulation  of  water  upon  the  fruit 
skin.  Charcoal  serves  the  same  purpose.  For  some 
fruits,  like  pears,  oat  chaff  or  rye  chaff  serves  better 
than  sawdust. 


VALUE   OF   CLEAN    SKIN  47 

This  absorption  of  moisture  explains  also  the  efficacy 
of  one  of  the  best  means  known  for  preventing  the  decay 
of  fruits.  Experience  of  recent  years  has  shown  that  the 
wrapping  of  fruits  with  paper  is  a  more  efficient  means 
of  protecting  them  from  the  ordinary  rot  than  almost  any 
device  that  has  ever  been  adopted.  There  may  be  two 
reasons  for  this.  Wrapping  the  fruit  with  paper  protects 
it  to  a  considerable  extent  from  mold  spores,  which  would 
drop  upon  the  skin  from  the  air  if  it  were  not  thus  pro- 
tected. But  this  is  doubtless  not  the  chief  reason  for 
the  value  of  the  paper  wrapper,  since  the  fruit  is  almost 
sure  to  be  infected  with  the  mold  spores  while  still  on  the 
trees,  and  certainly  before  it  can  be  wrapped  in  the  paper. 
The  paper  used  is  of  a  soft,  porous  nature,  and,  when  prop- 
erly wrapped  around  the  fruit,  absorbs  quickly  any  mois- 
ture that  may  be  upon  the  skin,  and  prevents  moisture  from 
further  condensation. 

Clean  Skin.  The  facts  mentioned  also  clearly  explain 
the  value  of  a  smooth  skin.  Since  decay  always  starts 
from  spores  that  lodge  on  the  skin,  any  method  of  pre- 
venting their  lodging  or  of  removing  them  will  protect 
the  fruit ;  hence  the  wiping  of  fruit  with  a  clean  cloth 
will  be  useful  in  protecting  it  from  decay.  Wiping  can- 
not, indeed,  wholly  remove  the  spores,  but  it  aids  materi- 
ally. Moreover,  if  the  wiping  is  done  with  a  dry  cloth,  it 
will  also  remove  the  moisture,  a  matter  of  no  small  impor- 
tance. Fruit  dealers,  who  have  learned  by  experience  how 
to  handle  fruit,  understand  well  that  a  frequent  wiping  of 
fruit  till  it  is  dry  and  clean  is  a  necessity  for  its  best 
preservation.  It  is  sometimes  surprising  to  see  in  what 
fine  condition  some  dealers  can  keep  fruit  far  into  the 


48  BACTERIA,  YEASTS,  AND   MOLDS 

spring  months  by  the  simple  devices  of  low  temperature 
and  clean,  dry  skins. 

Temperature.  We  have  already  noticed  how  effectively 
low  temperatures  check  the  growth  of  molds,  and  this 
applies  of  course  to  their  growth  in  fruit  as  well  as  else- 
where. If  fruits  could  be  actually  frozen,  the  decay  could 
be  indefinitely  prevented.  But  this  is  not  possible  with 
common  fruit,  since  the  freezing  injures  its  character.  All 
that  can  be  done,  therefore,  is  to-  cool  the  fruit  to  as  near 
the  freezing  point  as  possible  without  actually  freezing  it. 
If  the  temperature  is  lowered  until  the  fruit  is  near  to  the 
freezing  point,  the  growth  of  the  molds  may  be  so  delayed 
as  effectually  to  prevent  the  fruit  from  decaying  for  very 
many  months.  This  can  be  done  readily  in  the  modern 
cold-storage  plant,  and  in  the  last  few  years  fruit  growers 
have  been  learning  that  cold  storage  furnishes  a  means 
of  keeping  fruit  for  the  spring  market.  To  be  sure  the 
expense  of  such  storage  is  a  considerable  item,  but  the 
extra  price  that  may  be  received  in  the  spring  may  more 
than  make  it  good.  If  one  has  not  the  opportunity  for 
cold  storage,  it  is  best  to  keep  fruit  in  cool  cellars  where 
the  temperature  does  not  go  down  to  freezing  and  is  toler- 
ably constant.  The  lower  the  temperature  (above  freez- 
ing) the  better.  The  temperatures  of  cool  cellars  are  not, 
however,  low  enough  to  prevent  mold  growth  wholly. 
They  will  not  prevent  the  final  decay  of  the  fruit,  but 
they  are  very  useful  in  delaying  it.  When  fruits  are 
removed  from  such  cellars  it  must  be  remembered  that 
they  are  cold  and  will  condense  water  rapidly  on  their 
surfaces.  They  should  be  wiped  dry  after  being  in  the 
warm  air  a  few  hours,  or  they  will  decay  quickly. 


DECAY   DUE   TO    DISEASE 


49 


ROTTING  OF  FRUIT  DUE  TO  DISEASES  OF  THE 
FRUIT  TREE 

In  addition  to  the  rotting  of  fruit  due  to  the  growth 
of  common  molds,  it  is  important  to  know  that  many 
diseases  are  caused  by  certain 
microorganisms  that  attack  the 
plants  upon  which  they  are 
growing,  or  attack  the  fruits 
themselves  while  still  growing 
upon  the  fruit  trees.  These 
sometimes  produce  various 
kinds  of  rots  and  decay  in  the 
fruit  even  before  it  is  plucked 
(Fig.  26,  27).  In  some  cases  the 
fruit  may  appear  to  be  perfectly 
sound  when  picked  from  the 
tree,  but  it  is  really  already  in- 
fected with  molds  which  cause 
it  later  to  show  signs  of  decay 
(Fig.  21).  Nearly  all  of  the 
diseases  in  question  are  caused 
by  molds  somewhat  similar  to 
those  we  have  already  con- 
sidered, but  of  different  species. 
Botanists  know  a  large  number 
of  species  of  molds  which  grow  upon  different  fruit  trees, 
producing  diseases  of  the  tree  and  accompanied  by  decay 
of  the  fruit.  So  far  as  concerns  affairs  of  the  household 
these  imperfections  are  quite  beyond  the  reach  of  efficient 
remedies.  If  the  fruit  which  we  buy  at  the  market  and 


FIG.  26.  Peaches  turned  into 
a  hard  mass  (mummified)  by 
the  action  of  fungi. 


BACTERIA,   YEASTS,  AND    MOLDS 


bring  to  our  houses  is  already  infected  with  the  molds  in 
question,  nothing  that  we  can  do  will  protect  it  from  their 
subsequent  growth  and  consequent  decay.  The  only 
alleviating  remedy  is,  as  mentioned  in  other  cases,  to 
keep  the  fruit  cool,  because  none  of  these  microorganisms 
grow  readily  while  in  low  temperatures.  Dryness  is  of 
no  value,  since  the  molds  are  already  within  the  fruit, 

where  there  is  moisture 
enough. 

This  cause  of  the  de- 
cay of  fruit  is,  however, 
of  no  very  great  signifi- 
cance to  the  ordinary 
household,  because  in  a 
great  majority  of  cases 
the  fruits  infested  with 
these  troubles  will  show 
some  signs  of  decay  be- 
fore they  reach  the  mar- 
ket. The  loss  comes 

FIG.  27.     Peaches  decaying  on  the  tree.      uPon    tne    fruit    grower, 

upon  the  person  who  buys 

the  fruit  for  storing,  or  upon  the  dealer ;  rarely  will  the 
decay  thus  produced  be  delayed  sufficiently  for  the  fruit  to 
be  marketed,  sold,  and  carried  away  by  the  customers.  The 
consumer  would  not  distinguish  this  from  the  more  com- 
mon types  of  decay.  For  this  reason  this  species  of  fruit- 
disease,  while  of  great  significance  to  the  farmer  and  to 
the  one  who  handles  fruits,  is  of  no  very  great  impor- 
tance in  the  ordinary  household  and  need  not  here  be 
further  considered. 


USEFUL   MOLDS  51 

UTILITY  OF  MOLDS 

We  never  look  upon  molds  as  of  any  particular  utility. 
Nevertheless,  when  we  study  their  relations  in  nature  we 
find  that  they  are  of  the  utmost  importance.  In  the  pro- 
cesses which  are  going  on  in  nature  the  molds  form  a  very 
important  link,  aiding  in  furnishing  different  kinds  of  liv- 
ing beings  with  food.  The  woody  part  of  trees  contains 
a  large  amount  of  material  which  cannot  be  used  as  food 
by  either  plants  or  animals.  Were  it  not  for  some  agent 
which  brings  this  material  into  condition  for  subsequent 
use  by  plants  and  animals,  the  food  material  of  the  world 
would  in  time  become  stored  away  in  the  form  of  wood, 
and  the  world  would  materially  suffer  as  the  result.  But 
the  tree  trunk  does  not  remain  a  hard,  solid  mass  very 
long  after  it  has  fallen  to  the  ground.  It  slowly  softens 
and  decays,  until  eventually  it  assumes  a  condition  in 
which  it  can  again  be  used  for  food  by  various  animals 
and  plants.  Insects,  for  example,  feed  upon  the  decaying 
wood  until,  in  time,  the  tree  trunk  is  all  consumed.  In 
this  process  a  group  of  fungi  similar  to  molds  plays  an 
important  part,  for  it  is  a  mold-like  mycelium  growing 
through  the  hard  surface  of  the  wood  that  begins  the 
softening  necessary  to  make  its  utilization  possible.  With 
this  we  are  not  particularly  concerned,  for  the  household 
is  not  usually  concerned  in  the  decay  of  wood.  Wood  in 
the  household  may  occasionally  decay,  but  it  is  such  a  rare 
circumstance  that  the  housewife  pays  little  attention  to  it. 

Outside  of  their  agency  in  producing  the  decay  of  woods, 
molds  are  of  no  great  utility,  so  far  as  we  know  at  the 
present  time.  A  few  of  our  food  products  are,  however, 


52  BACTERIA,  YEASTS,  AND    MOLDS 

benefited  by  the  development  of  molds.  As  already 
noticed,  the  peculiar  flavor  of  certain  cheeses  is  due  to  the 
growth  of  molds.  Roqtiefort  cheese,  by  a  special  device 
of  the  manufacturer,  is  caused  to  mold.  When  cut  open 
this  cheese  shows  green  spots  extending  through  its  sub- 
stance, and  these  little  green  masses  are  simply  the  spores 
of  molds  which  have  developed  in  the  cheese  during  its 
ripening.  Stilton  cheese,  a  variety  made  in  England,  and 
Gorgonzola  are  also  ripened  by  molds.  Camembert  cheese, 
a  type  of  soft  cheese  very  popular  in  Europe  and  begin- 
ning to  obtain  a  considerable  market  in  the  United  States, 
is  always  covered  with  molds  which  have  developed  dur- 
ing the  ripening  of  the  cheese,  and  have  contributed  to 
its  flavor.  Brie  cheese  is  another  type  whose  flavors  are 
due  to  molds,  and  there  are  several  others  less  well  known. 

DISEASES  OF  ANIMALS  PRODUCED  BY  MOLDS 

Some  species  of  molds  may  live  a  parasitic  life.  Many 
species  live  as  parasites  upon  plants,  sending  their  myce- 
lium into  the  leaves  or  stems  of  the  plants,  and  produ- 
cing thus  a  variety  of  diseases.  With  these  we  are  not 
concerned  in  this  work.  A  few  molds  can  live  a  parasitic 
life  upon  animals,  and  there  are  consequently  a  few  animal 
diseases  produced  by  molds.  The  mold  diseases  of  man- 
kind are  confined  to  two  or  three  common  skin  diseases, 
which  sometimes  become  quite  troublesome. 

The  most  common  of  these  mold  diseases  in  man  is 
called  ringworm,  an  affection  of  the  skin  which  produces 
open  sores.  These  sores  spread  in  all  directions  from  a 
central  starting  point,  and  as  they  spread  they  heal  in 


MOLD   DISEASES 


53 


the  center,  though  continuing  to  spread  at  the  edge,  thus 
producing  a  ringlike  growth  that  has  given  origin  to  the 


FIG.  28.  A  mold  (Trie hop hy ton)  which  produces  ringworm.  At  a 
is  a  bit  of  hair  with  the  mold  spores  on  the  outside,  and  at  b  a 
figure  of  the  mold  itself  highly  magnified. 

name.  The  affection  is  a 
troublesome  one  to  heal, 
especially  when  it  gets  into 
the  scalp  ;  but  it  never  pro- 
duces  any  very  serious 
trouble.  Two  or  three  types 
of  this  disease  have  been 
found  to  be  produced  by 
two  or  three  kinds  of  molds. 
Fig.  28  shows  one  of  the 
common  species  that  is  the  FlG-,29:  . T™  pi\ces  of  ^r 'rom  the 

scalp  infested  with  a  mold  (Mtcrospo- 

cause  of  ringworm. 


At  a 

is  shown  a  bit  of  hair  with 
the  mold  fungus  and  mold 
spores  growing  upon  it,  and 
at  b  the  fungus  more  highly 
magnified.  Of  the  several  species  of  molds  that  produce 
this  trouble  some  are  more  liable  to  grow  upon  the  hair 


ron)  producing  ringworm.  The  upper 
figure  shows  the  masses  of  spores 
attached  to  the  outside  of  the  hair; 
the  lower  figure  shows  the  mold 
thread  lying  beneath  the  spores. 


54 


BACTERIA,  YEASTS,  AND  MOLDS 


and  others  upon  the  smooth  skin,  the  latter  proving  less 
troublesome  to  heal.  A  second  skin  disease  is  favus,  some- 
times difficult  to  distinguish  from  ringworm,  although  it  is 
produced  by  a  different  species  of  mold,  shown  in  Fig.  30. 
In  the  case  of  both  of  these  diseases  the  affection  is 
spread  by  means  of  mold  spores  discharged  through  the 

skin.  They  are  liable  to  be 
carried  from  person  to  person 
by  the  use  of  combs  or  towels, 
or  even  cloths  and  sponges 
used  in  washing  or  bathing 
the  skin.  If,  therefore,  there 
is  an  example  of  ringworm  in 
a  family,  it  is  imperative,  in 
order  to  prevent  the  spread 
of  the  disease  from  one  to 
FIG.  30.  A  mold  (Achorion)  pro-  another,  that  the  person  suf- 
ducing  a  second  type  of  skin  fering  from  the  attack  should 

disease  known  as  favus.    At  a     .  .  .  i         i  • 

..      .    ,  .  ...      have  his  own  combs,  his  own 

the  mycelium  is  shown,  at  b  the 

spores  as  found  on  hair.  towels,    his    Own    Sponges,    and 

even  his  own  soap  for  washing. 

By  this  means  the  disease  can  usually  be  confined  to  the 
person  in  whom  it  originally  appears.  The  cure  of  such 
diseases,  must  be  left  to  a  physician. 


MOLD-INFECTED  ROOMS 

Sometimes  a  room,  like  a  pantry,  may  become  badly 
infested  with  molds,  so  that  all  sorts  of  food  become 
rapidly  infected  by  them.  This  is  an  indication  that  the 
room  is  filled  with  mold  spores  in  such  numbers  that  they 


MOLD-INFECTED   ROOMS  55 

drop  into  everything  exposed.  The  remedy  for  such  con- 
dition is  to  get  rid  of  the  spores.  The  room  should  be 
vigorously  swept  and  dusted,  a  windy  day  being  chosen, 
and  all  windows  and  doors  should  be  left  wide  open  to 
blow  out  the  dust.  After  a  thorough  airing  the  room 
should  be  closed  again  and  left  undisturbed  until  the 
remaining  dust  settles ;  then  the  floor,  shelves,  window 
sills,  etc.,  should  be  wiped  with  a  damp  cloth.  This  will 
usually  remove  the  spores,  and  food  will  subsequently  be 
less  liable  to  mold. 


SECTION   II-  -YEASTS 

CHAPTER  V 

YEASTS  AND  THEIR  DISTRIBUTION 
FERMENTATION 

Yeasts  are  the  natural  agents  which  produce  the  phe- 
nomenon called  fermentation.  This  term  has  several  mean- 
ings to  the  scientists,  but  as  the  word  is  commonly  used 
it  refers  to  a  process  by  which  alcoholic  liquors  are  pro- 
duced from  sugary  solutions.  Fermentation  is  therefore 
the  basis  of  the  various  popular  beverages  known  to 
civilized  as  well  as  to  uncivilized  races.  Fermentation  is 
also  the  foundation  of  another  phenomenon  apparently 
quite  different  in  its  character ;  for  the  raising  of  bread  by 
yeast  is  just  as  truly  a  fermentation  as  is  the  manufacture 
of  beer. 

The  essential  phenomena  of  fermentation  are  the 
destruction  of  sugar  and  the  production  from  it  of  two 
other  substances.  The  sugar  is  originally  a  solid,  although 
it  is  very  easily  dissolved  in  water.  It  is  a  somewhat  com- 
plex body,  but  by  the  action  of  yeasts  it  is  easily  broken 
to  pieces  to  form  two  simpler  ones.  One  of  these,  alcohol, 
is  a  liquid  and  remains  in  solution  ;  the  other,  carbon  dioxide, 
is  a  gas  and  usually  passes  off  from  the  solution  in  the 
form  of  bubbles  (Fig.  31).  It  is  this  production  of  alcohol 

56 


FERMENTATION 


and  carbon  dioxide  that  is  the  foundation  of  all  fermenta- 
tive phenomena.  Chemists  represent  the  action  that  takes 
place  as  follows. 


(sugar) 


(alcohol)      (carbon  dioxide) 


The  phenomenon  of  alcoholic  fer- 
mentation has  been  known  for  many 
centuries,  traces  of  such  knowledge 
being  found  as  far  back  as  we  have 
any  recorded  history.  Back  in  the 
earliest  historical  days  mankind  was 
familiar  with  certain  fermented  drinks. 
At  the  present  time  we  find  that  the 
phenomena  of  fermentation  are  known 
by  nearly  all  races  of  men,  and  there 
is  hazily  a  tribe  of  savages  without 
its  own  kind  of  fermented  drink. 
These  "stimulating"  beverages  are  ob- 
tained from  a  variety  of  different 
materials  by  different  races.  The 
juice  of  grapes  has  long  been  used 
for  the  purpose,  but  various  other 
fruits  serve  equally  well.  The  juice 
of  the  palm  tree  is  used  by  some 
races,  and  sweet  juices  of  various 


•gas 


FIG.  31.  Fermenting  so- 
lution of  molasses, 
showing  at  a  the  grow- 
ing yeast  with  the  bub- 
bles of  carbon  dioxide 
arising,  and  also  the 
arrangement  for  con- 
ducting the  gas  under- 
neath limewater  at  b, 
for  the  purpose  of  de- 
termining the  nature 
of  the  gas. 

other  plants  are   also   used.     In   all 
cases  the  material  must  contain  sugar,  or  something  that 
can  be  converted  into  sugar ;  for  it  is  always  sugar  which 
undergoes  the  fermentation,  no  other  source  of  alcohol 
being  practical  for  producing  intoxicating  beverages.     In 


58  BACTERIA,   YEASTS,  AND    MOLDS 

the  process  of  bread  making,  too,  fermentation  has  been 
known  almost  as  long;  for  we  read  in  literature  of 
leavened  and  unleavened  bread  at  least  three  thousand 
years  ago. 

Although  fermentation  was  thus  long  known,  its  cause 
remained  a  mystery  until  the  nineteenth  century.  The 
type  of  fermentation  which  we  are  considering  is  in  all 
Ceases  produced  by  essentially  the  same  agency,  a  group 
of  plants  called  yeasts.  It  is  not  always  the  same  species 
of  yeast,  for  the  group  includes  quite  a  large  number  of 
different  species.  The  commercial  product  is  simply  one 
kind  that  has  been  cultivated  for  commercial  purposes ; 
but  there  are  many  others  in  nature  not  under  cultivation 
which  may  conveniently  be  called  wild  yeasts.  All  of  the 
kinds  are,  however,  very  similar  in  appearance,  have  the 
same  general  characters,  and  are  closely  related  to  each 
other. 

Yeast  was  discovered  about  two  centuries  ago  by  a 
Dutch  microscopist,  who  found  fermented  liquors  filled 
with  minute  bodies,  the  significance  of  which  he  did  not 
understand.  Nor  were  they  really  appreciated  until  about 
the  third  decade  of  the  nineteenth  century.  At  that  time 
it  was  quite  conclusively  demonstrated  that  these  minute 
bodies  were  living  organisms,  capable  of  feeding,  growing, 
and  multiplying,  and  having  a  very  close  relation  to  the 
phenomena  of  fermentation.  It  was  soon  shown  also 
that  it  was  their  growth  that  produced  the  fermentation, 
since  this  phenomenon  would  not  occur  unless  these 
organisms  were  not  only  present  but  also  growing  and 
multiplying.  In  our  study  we  must  first  learn  the  nature 
of  the  yeast  plant. 


STRUCTURE   OF   YEASTS 


59 


WHAT  ARE  YEASTS 

Yeast  plants  are  always  microscopic,  no  species  being 
large  enough  to  be  seen  with  the  naked  eye.  When  these 
tiny  plants  are  massed  together,  as  in  a  yeast  cake,  the 
mass  may  form  a  bulk  large  enough  to  be  seen.  We  can 
see  a  yeast  cake, 
but  the  individual 
yeast  plant  is  not 
more  than  ^  of  an 
inch  in  diameter, 
and  this  is  far  be- 
low the  power  of 
the  unaided  vision. 
By  the  microscope 
alone  we  learn  that 
the  yeast  mass  is 
made  up  of  millions 

Of    minute    bodies,    FlG;  32-     Common  yeast  very  highly  magnified. 
.  Figs,  a  and  b  show  vacuoles;  c  shows  a  nucleus 

each  of  which  is  an      n  inside  of  the  yeast  cell;  d  shows  a  budding 

individual  yeast  cell  with  the  nucleus  dividing ;  e  shows  the  cell 
r>lant  divided,  the  new  cell  containing  a  bit  of  the 

old  nucleus. 

The  yeast  plants 

are  much  simpler  than  the  molds.  If  a  bit  of  a  yeast 
cake  be  mixed  with  a  little  water  and  examined  under 
the  microscope,  there  will  be  found  what  is  shown  in 
Fig.  32.  There  will  be  seen  large  numbers  of  minute 
oval  bodies,  sometimes  very  nearly  spherical  or  sometimes 
considerably  longer  than  broad.  They  are  quite  color- 
less and  nearly  transparent,  as  seen  under  the  micro- 
scope, but  whitish  when  seen  in  bulk.  They  have  a 


60  BACTERIA,   YEASTS,  AND    MOLDS 

uniform,  smooth  outline,  but  inside  of  them  may  com- 
monly be  seen  some  smaller  bodies.  There  is  usually 
a  somewhat  rounded  clear  spot,  as  shown  in  Fig.  32,  a> 
although  in  many  cases  instead  of  one  we  find  two,  three, 
or  four  smaller  ones  (Fig.  32,  b).  These  apparently  rep- 
resent only  little  drops  of  an  oily  liquid  and  have,  so  far 
as  we  know,  nothing  very  particular  to  do  with  the  life  of 
the  yeast  plant.  These  drops  are  called  vacucles.  No 
further  bodies  can  be  seen  in  the  yeast  cell  by  ordinary 
methods  of  study,  although  special  microscopic  devices 
show  that  there  are  other  bodies  inside  (Fig.  32,  c).  These 
other  smaller  bodies  need  not,  however,  concern  us.  The 
yeast  cell  thus  described  is  quite  unlike  ordinary  plants, 
showing  less  resemblance  to  them  than  molds.  But  though 
they  bear  no  likeness  to  what  we  commonly  call  plants, 
biologists  are  unanimous  in  their  opinion  that  they  are  to 
be  classed  with  the  molds  as  colorless  plants  and,  hence, 
as  fungi. 

Yeast  exists  in  three  somewhat  different  states:  (i)  the 
resting  state ;  (2)  the  growing  state ;  (3)  the  spore- 
bearing  state.  The  yeast  in  an  ordinary  yeast  cake 
already  described  is  in  the  resting  state.  Such  yeast 
appears  as  in  Fig.  32,  a,  each  plant  being  a  single  oval 
body  or  cell.  It  is  alive  but  is  not  actively  growing. 

The  Growing  State.  When  a  little  resting  yeast  is 
placed  in  a  solution  which  contains  proper  material  for 
food  it  begins  at  once  to  consume  the  food  and  grow. 
As  it  grows  it  multiplies  by  a  method  known  as  budding. 
Upon  the  sides  of  the  yeast  plants  appear  small  buds  (Fig. 
33,  a).  Each  bud  at  first  appears  as  a  little  swelling  on 
the  side  of  the  larger  yeast  cell.  This  little  bud  increases 


STRUCTURE   OF   YEASTS 


6l 


in  size  until  finally  it  may  be  as  large  as  the  original  plant 
(Fig.  33,  c).  Usually  by  this  time,  if  the  growth  is  vigor- 
ous, there  may  have  appeared  a  second  bud.  The  latter 
sometimes  arises  from  the  side  of  the  first  cell  and  some- 
times from  the  side  of  the  first  bud,  giving  an  appearance 
such  as  is  shown  at  Fig.  33,  c.  This  budding  continues, 
the  little  buds  appearing  one  after  the  other,  until  there 
are  produced  irregular-shaped  groups  like  those  shown  at 
Fig.  33,  d.  For  a  considerable  time  the  cells  in  these 
groups  remain  attached  to  each  other,  so  that  a  little  of 
the  sediment  from 
a  fermenting  liquid 
will  appear  under 
the  microscope  as 
shown  in  Fig.  33,^. 
After  a  while,  how- 
ever, the  different 
cells  drop  apart 
and  may  go  into 
a  resting  stage,  each  cell  remaining  by  itself.  These 
cells  are  capable  of  growth  and  development,  either  imme- 
diately or  subsequently,  when  again  placed  in  a  solution 
which  furnishes  them  food.  This  method  of  multipli- 
cation, which  is  distinctly  characteristic  of  yeasts  and 
separates  them  sharply  from  bacteria,  the  next  group  of 
plants  to  be  studied,  is  known  as  budding.  "The  yeast 
plants  are  therefore  sometimes  called  the  budding  fungi. 

The  Spore-bearing  State.  Under  some  conditions  yeast 
plants  produce  a  different  kind  of  reproductive  body  known 
as  spores.  If  a  lot  of  yeast  is  placed  where  it  has  mois- 
ture but  insufficient  food,  it  does  not  grow  by  the  normal 


FIG.  33.     Growing  yeast  cells,  showing  method 
of  budding  and  forming  groups  of  cells. 


62 


BACTERIA,   YEASTS,  AND   MOLDS 


FIG.  34. 

containing    four 
spores. 


method  of  budding,  but  its  contents  break  up  into  several 

parts.  In  Fig.  34  is  shown  one  of  these  yeast  cells  which 
has  been  growing  on  a  porcelain  plate 
without  sufficient  nourishment,  and  it 
will  be  seen  that  four  small  bodies 
have  formed  inside  of  the  cell.  These 
bodies  are  spores  and  are  capable  of 
A  yeast  cell  resisting  for  a  long  time  a  variety  of 
adverse  conditions,  such  as  drying, 
heating,  etc.,  without  being  injured. 

When  the  yeast  cell  breaks,  the  little  spores  burst  forth 

ready  to  be  distributed   by  the  winds  or  by  any  other 

convenient  means. 

Not  all  species  of 

yeasts  are  yet 

known  to  produce 

spores  of  this  kind, 

although  it  is  a 

characteristic  pos- 
sessed by  a  large 

number  (Fig.  35). 

Botanists  divide       FlG-  35-     Three  species  of  yeast  each  contain- 
ing spores. 

yeasts  into  two 

divisions  in  accordance  with  their  power  of  producing  such 
spores.  The  genus  Saccharomyces  includes  yeasts  which 
produce  spores,  while  the  genus  Torula  includes  those  that 
do  not.  The  number  of  spores  formed  in  a  single  yeast 
cell  is  not  always  the  same,  although  commonly  three  or 
four.  It  may  not  always  be  the  same  for  the  same  species 
of  yeast. 


DISTRIBUTION    OF   YEASTS  63 

WHERE  YEASTS  ARE  FOUND 

From  the  facts  just  mentioned  it  will  readily  be  under- 
stood that  yeasts  have  a  wide  distribution,  even  though 
they  do  not  grow  luxuriantly  except  in  sugar  solutions. 
The  spores  are  excessively  minute  and  are  capable  of 
being  thoroughly  dried  without  injury,  in  which  condition 
they  will  remain  alive  for  months.  These  spores  are 
easily  blown  by  the  winds  and  distributed  far  and  wide. 
Even  the  bodies  of  the  yeast  cells  in  their  resting  stage, 
before  they  have  produced  spores,  may  be  dried,  and  for 
considerable  time  suffer  no  injury.  These  dry  yeast  cells 
will  keep  for  weeks  and  sometimes  for  months  without 
losing  their  power  of  growth.  The  commercial  dried 
yeast  cake,  which  will  be  referred  to  presently,  contains 
not  yeast  spores  but  simply  dried  yeast  cells.  These  are 
still  alive  and  remain  for  a  long  time  capable  of  growing 
if  placed  in  proper  conditions  of  food  and  moisture.  Such 
dried  yeast  cells  are  very  light  and  easily  distributed  by 
currents  of  air.  In  such  dried  form  yeast  is  distributed 
in  dust  by  the  winds,  and  may  be  found  almost  univer- 
sally present  over  the  surface  of  the  earth,  except  in  the 
middle  of  oceans  and  deserts.  Elsewhere  the  air,  the 
soil,  and  the  water  are  practically  sure  to  contain  yeast 
in  greater  or  less  abundance. 

Such  yeast  plants,  or  yeast  spores,  blowing  around  in  the 
air  have  sometimes  been  called  wild  yeast,  a  name  quite 
convenient  for  distinguishing  plants  which  are  indiscrimi- 
nately scattered  in  the  air  from  those  which  we  cultivate  in 
great  masses  for  purposes  of  brewing,  bread  making,  etc. 


64  BACTERIA,  YEASTS,  AND   MOLDS 

Spontaneous  Fermentation.  These  wild  yeasts  are  so 
common  in  the  air  that  they  are  sure  to  be  present  in 
most  localities,  and  they  fully  explain  certain  phenomena 
of  fermentation  that  seem  at  first  sight  somewhat  puz- 
zling. Almost  any  sugary  solution  will  contain  them.  If 
the  juice  of  an  apple  is  squeezed  from  the  pulp,  it  forms 
a  sweet  liquid  which  tastes  at  first  almost  exactly  like 
the  apple  from  which  it  is  taken.  But  if  it  is  allowed  to 
stand  in  a  warm  place  a  fermentation  begins  in  it  which 
rapidly  changes  its  character,  pro- 
ducing in  a  few  hours  what  we  call 
cider.  A  typical  alcoholic  fermen- 
tation has  started,  just  as  truly  due 
to  the  growth  of  yeast  as  are  similar 
fermentations  in  a  brewery.  Since 
the  yeast  has  not  been  planted  con- 

FIG.  3^  Wild  yeast  from  Sci°Uslv  in  the  dder>  the  fermenta- 
the  juice  of  an  apple,  tion  must  be  due  to  the  wild  yeasts 
which  causes  the  fermen-  which  find  their  way  into  the  juice, 

tation  of  cider.  either  ^^  ^   ^  been  squeezed 

from  the  apple  pulp  or  afterwards.  The  apple  has  been 
growing  in  the  air  for  many  weeks,  and  the  wild  yeasts 
have  had  plenty  of  chances  to  lodge  on  its  skin.  When  the 
juice  is  squeezed  from  the  pulp  it  is  sure  to  contain  these 
yeasts,  and  they  promptly  start  a  fermentation  (Fig.  36). 

In  a  similar  way  other  spontaneously  fermented  prod- 
ucts are  made  from  the  juice  of  various  plants  or  fruits ; 
for  any  sweet  juice  from  such  natural  sources  will  be  sure 
to  become  inoculated  with  wild  yeast  and  will  consequently 
undergo  fermentation.  This  fact  has  been  learned  by 
almost  all  people  from  experience.  Most  savage  tribes 


SPONTANEOUS  FERMENTATION        65 

have  learned  to  make  fermented  drinks  from  the  juices  of 
plants  or  fruits  by  simply  collecting  the  sweet  liquor  and 
allowing  it  to  stand  until  it  ferments. 

These  wild  yeasts  explain  another  phenomenon  occa- 
sionally seen  in  the  household.  The  housewife  finds  that 
some  of  her  preserved  fruits  or  jellies  at  times  undergo 
an  alcoholic  fermentation.  This  is  quite  different  from 
molding  or  decay,  and  is  found  only  in  sugar-holding 
materials.  The  preserve  develops  a  peculiar,  sharp,  pun- 
gent taste,  easily  recognized  but  difficult  to  describe.  It 
is  particularly  liable  to  occur  in  jellies,  partly  because 
they  contain  much  sugar  and  partly  because,  even  when 
covered  in  jelly  tumblers,  they  are  still  somewhat  exposed 
to  the  air  and  hence  are  liable  to  inoculation  with  wild 
yeast.  Sometimes  this  phenomenon  is  also  found  in 
canned  foods  that  have  not  been  properly  protected.  It 
is  not  uncommon  to  find  a  similar  fermentation  occurring 
in  certain  types  of  sugar.  Maple  sugar  which  is  kept  in 
the  pantry  for  weeks  until  it  becomes  moist,  may  ferment 
and  develop  the  peculiar  sour  taste  characteristic  of  this 
phenomenon.  In  all  such  cases  the  trouble  is  due  to 
the  presence  of  the  wild  yeasts  which  are  floating  in 
the  air  and  which  settle  and  grow  upon  any  proper  food. 
These  wild  yeasts  are  so  sure  to  be  present  in  the  air 
that  it  is  very  difficult  to  protect  a  fermentable  material 
from  their  action  unless  the  air  is  completely  excluded. 

Such  wild  yeasts  do  not,  of  course,  live  permanently  in 
the  air,  since  the  air  would  itself  furnish  no  food  for  them. 
They  live  and  grow  in  the  soil,  in  decaying  fruit  on  the 
ground,  on  the  surface  of  fruit  on  the  trees,  and  in  a 
variety  of  other 'places.  The  air  simply  distributes  them. 


66  BACTERIA,  YEASTS,  AND    MOLDS 

FOOD    REQUIRED    BY    YEAST 

All  common  species  of  yeast  require  sugar  for  food, 
and  therefore  will  not  grow  rapidly  unless  sugar  is  pres- 
ent in  abundance.  Bread  dough  ferments  because  it  con- 
tains some  sugar.  Flour  itself  contains  a  large  amount 
of  starch,  which  is  not  fermentable ;  but  in  the  bread 
dough  some  of  the  starch  is  changed  to  sugar  by  a  chem- 
ical process,  so  that  fermentation  is  possible.  Almost  all 
sugar  solutions  furnish  a  proper  medium  for  yeast  growth, 
provided  the  solution  is  not  too  dense.  Yeast  cannot  live 
upon  absolutely  pure  sugar,  since  it  needs  certain  other 
materials  for  food ;  but  all  natural  sugar  solutions,  such 
as  molasses,  grape  juice,  etc.,  contain  quite  enough  other 
material  for  the  yeasts  to  feed  upon,  and  they  ferment 
readily  enough.  A  high  percentage  of  sugar  is  injurious 
to  the  growth  of  yeasts,  a  fact  that  explains  why  almost 
anything  can  be  preserved  if  it  is  saturated  with  a  large 
amount  of  sugar.  (See  Preserves,  p.  163.) 

Food  is  required  for  yeasts  during  the  fermentation, 
since  they  are  growing  and  rapidly  increasing  in  abun- 
dance. The  simple  presence  of  yeasts  produces  no  fer- 
mentation. If  anything  prevents  the  growth  of  the  yeast 
plants,  no  fermentation  occurs,  and  it  is  always  found  that 
the  yeast  increases  in  bulk  during  the  process.  In  the 
large  fermentative  industries  there  is  consequently  pro- 
duced a  large  quantity  of  yeast,  which  accumulates  in 
bulk  at  the  close  of  the  fermentations. 

This  material  has  been  mostly  a  waste  product,  although 
a  considerable  amount  of  it  has  been  utilized  for  bread 
raising,  as  shown  in  the  next  chapter.  Recently  a  new 


FOOD   OF    YEAST  67 

use  for  such  masses  of  yeast  plant  has  been  suggested. 
The  yeast  mass  must  contain  considerable  food  material, 
and  the  question  has  been  raised  whether  it  is  not  pos- 
sible to  utilize  it  as  a  food  product.  By  simple  means 
extracts  of  such  yeasts  have  been  made  and  have  lately 
been  placed  upon  the  market.  These  materials,  known 
as  ovits,  wukj  and  siris,  have  not  yet  appeared  in  America 
but  are  found  in  the  European  trade.  They  have  a  value 
almost  the  same  as  that  of  ordinary  beef  extracts.  They 
make  an  appetizing  bouillon  which  may  be  a  useful  stimu- 
lant, but  since  they  are  only  extracts,  they  contain  practi- 
cally no  real  food.  They  may  therefore  easily  take  the 
place  of  such  substances  as  Liebig's  beef  extract  and  similar 
products,  but  like  them  they  do  not  contain  real  food  and 
must  not  be  regarded  as  nutritious. 


CHAPTER  VI 
YEASTS  IN  THE  HOUSEHOLD 

As  Enemies.  Yeast  must,  in  general,  be  looked  upon  as 
the  housewife's  friend,  since  in  almost  all  its  relations  to 
household  affairs  it  produces  only  desirable  results.  In  a 
few  instances  we  find  yeast  producing  trouble.  Its  occa- 
sional presence  in  jellies  and  preserves  has  already  been 
noticed,  as  well  as  in  the  fermentation  of  maple  sugar. 
*•  Any  sirup  containing  fruit  sugar,  cane  sugar,  or  beet 
sugar  may  undergo  spontaneous  fermentation  in  our 
homes.  In  dairy  products  yeasts  occasionally  produce 
mischief,  since  the  bitter  tastes  of  milk  and  cheese  are 
sometimes  caused  by  their  growth.  This  will  rarely  if 
ever  trouble  the  housewife,  although  it  may  cause  mis- 
chief for  the  dairymen.  *  It  is  only  in  the  fermentation  of 
sugary  substances,  like  jellies  and  sirups,  th#t  the  house- 
wife is  troubled  with  undesired  fermentation.  One  prac- 
tical suggestion  in  this  connection  may  be  of  use.  Since 
boiling  will  kill  yeasts,  any  material  which  shows  the  easily 
recognized  sign  of  fermentation  —  the  peculiar,  sharp, 
pungent  taste  —  can  be  preserved  from  further  injury  if 
it  is  merely  heated  to  the  temperature  of  boiling.  No 
further  fermentation  will  then  occur,  provided  the  subse- 
quent entrance  of  yeast  is  prevented  by  protecting  the 
material  from  the  air.  If  the  material  cannot  be  heated, 
there  is  no  satisfactory  remedy  for  a  fermentation  once 
started. 

68 


YEASTS   A   SOURCE   OF  ALCOHOL  69 

As  Friends.  Yeasts  must  usually  be  looked  upon  as 
servants  rather  than  as  enemies.  They  are  the  allies  of 
the  housewife  in  a  number  of  directions.  We  have 
noticed  above  that  when  they  grow  in  sugar  solutions 
they  give  rise  to  two  new  substances,  carbon  dioxide  and 
alcohol,  and  in  various  domestic  affairs  sometimes  the 
one,  sometimes  the  other,  and  sometimes  both  of  these 
products  are  utilized. 

THE  USE  OF  YEASTS  AS  A  SOURCE  OF  ALCOHOL 

The  alcohol  produced  by  yeasts  is  the  foundation  of  the 
great  fermentative  and  distillery  industries,  for  common 
yeasts  are  the  agents  which  produce  the  alcohol  found  in 
all  alcoholic  beverages.  The  fermentative  industries,  of 
immense  extent  all  over  the  civilized  world,  are  dependent 
upon  yeasts.  In  the  manufacture  of  fermented  and  dis- 
tilled liquors  these  little  plants  are  used  in  all  cases  for 
the  production  of  alcohol  out  of  various  sugar  solutions. 
The  fermentative  industries,  therefore,  involving  the  invest- 
ment of  hundreds  of  millions  of  dollars,  are  founded  upon 
the  growth  and  powers  of  these  microscopic  plants.  The 
struggle  with  gigantic  evils  resulting  from  these  industries 
forms  one  of  the  greatest  problems  of  civilization.  This, 
however,  is  a  matter-  which  does  not  belong  to  our 
immediate  subject. 

In  breweries  and  distilleries  some  material  containing 
sugar  (molasses,  preparations  from  rye,  corn,  barley,  etc.) 
is  inoculated  with  a  quantity  of  yeast,  a  species  being- 
chosen  which  experience  has  shown  to  be  well  adapted 
to  the  purpose.  The  mixture  is  warmed  slightly  and  a 


70  BACTERIA,  YEASTS,  AND    MOLDS 

vigorous  fermentation  is  started.  The  fermented  mass 
may  subsequently  be  used  directly  for  a  beverage — fer- 
mented drinks,  like  beer,  ale,  etc.  —  or  the  water  may  be 
partly  separated  from  the  alcohol  by  distillation,  produ- 
cing a  liquor  with  a  much  higher  percentage  of  alcohol, — 
the  distilled  liquors,  like  rum,  brandy,  whisky,  etc. 

In  the  making  of  wines  the  process  is,  in  a  way,  simpler, 
and  reliance  is  usually  placed  upon  the  wild  yeasts  which 
produce  a  spontaneous  fermentation.  The  skin  of  the 
grape  becomes  the  lodging  place  of  numerous  micro- 
organisms which  collect  there  while  the  grape  is  growing. 
These  include  molds  and  bacteria  as  well  as  yeasts,  and 
when  the  juice  is  squeezed  from  the  grape  it  is  certain  to 
contain  some  of  this  wild  yeast.  Fig.  37  shows  some  of 
the  wild  yeast  thus  spontaneously  inoculated  into  grape 
juice.  The  juice  is  set  aside  and  a  spontaneous  fermen- 
tation begins.  The  fermentation  is  not  very  vigorous  and 
may  require  many  weeks  for  its  completion.  In  recent 
years  some  vintners  have  adopted  the  plan  of  adding  to 
the  grape  juice  cultures  of  chosen  varieties  of  yeast  for 
the  purpose  of  hastening  the  fermentation  and  making  it 
more  reliable.  The  success  of  the  plan  is  still  somewhat 
doubtful,  and  this  method  of  wine  making  has  not  been 
very  widely  adopted  up  to  the  present  time. 

So  sure  is  the  grape  juice  to  contain  yeasts  that  unless 
some  means  of  preventing  their  growth  is  adopted  fer- 
mentation cannot  be  avoided.  In  making  what  is  called 
unfermented  grape  juice  the  yeasts  are  destroyed  by  heat. 
The  grape  juice  is  heated  to  a  temperature  of  about 
170°  for  a  few  minutes.  This  operation  is  usually  per- 
formed twice,  after  which  the  wine  is  bottled  and  sealed. 


YEASTS  A  SOURCE   OF  ALCOHOL  71 

The  process  is  really  the  same  as  that  of  preserving 
food  by  canning,  which  will  be  described  later,  the  only 
essential  difference  being  that  the  grape  juice  does  not 
require  boiling  for  its  preservation.  It  will  be  noticed 
from  Fig.  37  that  there  are  other  organisms  besides 
yeasts  upon  the  grape  skin.  These  may  have  some  effect 
upon  the  wine,  but  very  little  is  known  in  regard  to  the 
matter. 

In  the  household  yeasts  are  occasionally  used  in  the 
same  way,  solely  for  the  alcohol  they  develop.  This  use 
is  practically  confined  to  the 
manufacture  of  a  few  of  the 
homemade  wines  which  are 
produced  from  juices  of  fruit 
such  as  grapes,  elderberries, 
blackberries,  currants,  rasp- 
berries, etc.  Cider  also  is  an 
apple  wine.  The  principles 
in  the  manufacture  of  these 
homemade  wines  are  the  FIG.  37.  Organisms  found  upon  the 

same  as  in  the  production  of  skin  of  a  grape  and  concerned  in 
the  commercial  wines.  The  the  fermentation  of  wine. 

fruit  juice,  which  contains  a  considerable  quantity  of  easily 
fermentable  sugar,  is  expressed  from  the  fruits  and  mixed 
with  water.  Commonly  the  fruit  juice  is  not  sweet  enough, 
particularly  if  a  sweet  wine  is  desired.  In  the  manufac- 
ture of  most  homemade  wines,  therefore,  sugar  is  added. 
The  amount  varies  widely  with  the  kind  of  fruit  used, 
being  greater  for  sour  fruits,  and  it  varies  also  according 
to  whether  a  sweet  or  sour  wine  is  wanted.  The  juice  is 
then  left  to  ferment  spontaneously  under  the  influence  of 


72        BACTERIA,  YEASTS,  AND  MOLDS 

wild  yeasts.  The  juice  must  not,  of  course,  be  heated, 
for  this  would  kill  the  yeasts  and  prevent  fermentation. 
The  fermentation  is  not  very  vigorous,  and  the  amount 
of  alcohol  developed  not  very  great.  After  the  fermenta- 
tion has  about  stopped,  the  wine  is  placed  in  bottles  or  in 
closed  casks.  The  time  required  for  fermentation  may  be 
a  few  weeks  (currant  wine)  or  many  months  (grape  wine). 
In  making  cider  nothing  is  necessary  except  to  press  the 
juice  from  the  apples  and  allow  it  to  ferment  sponta- 
neously. Fermentation  in  any  of  these  cases  might  be 
hastened  by  the  addition  of  yeast.  This  is  occasionally 
done,  but  is  not  a  common  practice. 

Whatever  be  the  source  of  the  yeast,  the  process  of 
wine  making  is  simply  an  ordinary  fermenting  of  the 
sugar.  The  carbon  dioxide  that  is  produced  is  allowed  to 
pass  off  into  the  air  undisturbed  during  the  fermentation, 
and  the  liquid  gradually  becomes  filled  with  alcohol.  The 
final  result  is  the  wine,  which  always  contains  alcohol  in 
small  percentage.  After  the  yeasts  stop  growing,  bacteria 
may  develop  in  the  product  and  cause  further  changes, 
so  as  to  injure  its  taste,  or  even  totally  change  its  nature, 
as  in  the  formation  of  vinegar.  (See  Chapter  IX.) 

Y  THE  USE  OF  YEASTS  AS  A  SOURCE  OF  CARBON 
DIOXIDE 

The  chief  use  of  yeasts  in  the  household  is  not  to  pro- 
duce fermented  drinks  but  to  raise  bread.  The  raising 
of  bread  by  means  of  yeast  has  been  brought  to  a  state  of 
great  perfection,  so  that  the  method  of  producing  a  desir- 
able fermentation  in  bread  dough  by  means  of  this  product 


YEAST  AS  A  SOURCE  OF  CARBON  DIOXIDE   73 

is  now  extremely  simple.  But  it  has  taken  many  centuries 
of  experiment  and  trial  to  understand  the  subject  well 
enough  to  bring  it  under  proper  control 

In  all  nations,  and  apparently  in  all  ages,  people  have 
been  accustomed  to  make  bread  from  meals  obtained  from 
the  different  kinds  of  grain.  The  earliest  method  of  cook- 
ing such  material  was  simply  to  mix  it  with  water  and 
then  bake  it,  the  result  being  a  rather  hard,  tough  material 
known  as  unleavened  bread. 

The  next  step  consisted  of  a  spontaneous  raising  of  the 
dough.  If  dough  is  left  in  a  warm  place  for  a  number  of 
hours,  it  becomes  somewhat  swollen  with  gas,  appears 
lighter  in  character,  and  when  baked  produces  a  type  of 
bread  more  easily  masticated,  better  in  flavor,  and  more 
easily  digested.  Flour  from  most  cereals,  if  mixed  with 
water  and  kept  for  a  few  hours  in  a  warm  place,  will 
undergo  a  fermentation,  due  to  the  wild  yeasts  that  may 
have  found  entrance  to  the  meal.  This  method  of  fer- 
menting the  dough  gave  the  first  form  of  raised,  or  leav- 
ened bread. 

Very  early,  even  before  historical  records,  it  was  dis- 
covered that  a  little  of  the  dough  thus  raised  would  serve 
as  a  starter  for  a  second  batch,  resulting  in  a  quicker  and 
more  satisfactory  raising  than  that  obtained  by  spontane- 
ous fermentation.  This  was  known  as  leaven,  and  as  far 
back  as  the  time  of  Lot  we  read  of  leavened  and  unleav- 
ened bread.  The  Egyptians  also  knew  of  this  process. 
Leaven  has  been  used  from  those  early  days  to  the  pres- 
ent time.  Even  to-day  leaven  consists  of  a  little  dough 
which  has  already  fermented  and  hence  contains  yeasts, 
and  which  is  saved  to  be  used  in  fresh  dough  for  the 


74  BACTERIA,  YEASTS,  AND   MOLDS 

purpose  of  starting  fermentation.  Although  its  use  has 
largely  given  way  to  cultivated  yeast,  it  has  been  employed 
in  the  baking  of  bread  up  to  very  recent  times,  and  to  a 
limited  extent  is  still  used  in  France.  The  difficulty 
with  leaven  is  that  its  action  is  unreliable.  The  leaven 
contains  bacteria  as  well  as  yeast,  and  these  may  make  the 
bread  sour,  or  sometimes  bitter;  and  unless  the  very 
greatest  care  is  taken  in  its  manipulation  the  bread  pro- 
duced by  means  of  it  is  not  good.  Only  very  skillful 
bakers  can  use  it  satisfactorily.  The  use  of  leaven  has, 
therefore,  almost  wholly  been  replaced  by  the  far  more 
easy  and  reliable  method  of  raising  dough  with  cultivated 
yeasts. 

The  use  of  yeast  instead  of  leaven  in  bread  making  is 
also  old.  In  the  time  of  the  Roman  empire  it  is  apparent, 
from  a  few  references  in  literature,  that  the  use  of  yeast 
was  understood.  It  is  stated  that  the  Romans  in  baking 
their  bread  sometimes  used  a  leaven  made  of  grape  juice 
and  millet  for  the  purpose  of  hastening  fermentation. 
We  have  already  seen  that  grape  juice  is  sure  to  contain 
yeast,  and  this  phenomenon,  whose  nature  the  Romans, 
of  course,  did  not  understand,  is  perfectly  intelligible 
to-day.  The  Romans  were  unconsciously  using  yeast  for 
raising  their  bread.  The  early  bakers  soon  learned  to  use 
yeast  in  a  more  accurate  and  satisfactory  manner,  and 
from  the  time  of  Rome  down  through  the  centuries  the 
use  of  cultivated  yeast  products  for  the  purpose  of  raising 
bread  was  more  or  less  common.  The  methods  of  pro- 
ducing and  cultivating  yeast  during  these  various  ages  are 
not  known  at  the  present  time.  It  is  known,  however, 
that  later  the  use  of  yeast  declined,  and  bakers  returned 


METHODS    OF   OBTAINING   YEAST  75 

to  the  old  method  of  using  leaven.  In  the  seventeenth 
century  the  use  of  yeast  began  again,  and  from  that 
time  on  it  has  been  used  more  and  more  widely.  As 
methods  of  cultivating  yeast  developed  it  became  pos- 
sible to  obtain  a  more  reliable  product,  and  as  the  relia- 
bility of  the  product  increased  so  did  its  usefulness  in  a  pro- 
portionate degree.  At  the  present  time  yeast  has  very 
largely  taken  the  place  of  leaven  in  baking,  because  it  has 
proved  easier  to  handle  and  more  reliable  in  its  results. 

METHODS  OF  OBTAINING  YEAST 

The  original  source  of  all  forms  of  cultivated  yeast  is 
wild  yeast,  which,  as  we  have  seen,  may  easily  be  obtained 
by  exposing  any  sugary  solution  to  the  air.  To  obtain 
such  yeast  in  quantity  sufficient  for  the  purposes  of  house- 
hold fermentation,  various  devices  have  been  practiced. 
Some  of  these,  though  little*  used  at  present,  are  instruct- 
ive. A  very  interesting  method  of  obtaining  yeast  called 
"salt  raising"  was  frequently  practiced  by  housewives 
before  the  introduction  of  compressed  yeast.  To  a  quan- 
tity of  milk  was  added  a  little  salt,  sufficient  to  delay 
the  growth  of  the  common  bacteria  which  otherwise 
quickly  sour  it.  The  milk  was  then  placed  in  a  warm 
place  for  several  hours.  The  yeasts  which  found  entrance 
from  the  air  were  not  injured  by  the  salt,  and  grew  rapidly. 
The  milk  soon  began  to  froth  from  the  carbon  dioxide  thus 
developed.  This  material  was  then  used  to  mix  with  the 
dough  for  the  raising.  The  method  here  described  has 
nearly  gone  out  of  use,  and  no  study  has  been  made  of 
the  kinds  of  microorganisms  actually  concerned  in  the 


76  BACTERIA,  YEASTS,  AND   MOLDS 

process,  though  it  probably  involved  both  yeasts  and  bac- 
teria. It  is  interesting  to-day  simply  because  it  was  a 
method  of  utilizing  the  wild  microorganisms  for  the  pur- 
pose for  which  we  now  use  cultivated  yeasts. 

Other  devices  obtained  by  spontaneous  fermentation 
have  frequently  been  practiced.  Bakers  sometimes  make 
a  brew  which  is  allowed  to  ferment  spontaneously,  and 
use  the  product  for  bread  raising.  In  making  the  Scotch 
barms,  a  brew  is  prepared  containing  hops  and  flour,  with 
other  ingredients,  and  this,  at  least  in  making  "  virgin 
barm,"  is  allowed  to  ferment  spontaneously. 

In  all  such  cases  yeasts  are  obtained,  but  they  are 
always  mixed  with  bacteria,  which  may  materially  inter- 
fere with  their  successful  working.  The  uncertainty  of 
results  due  to  these  impurities  has  led  to  cultivating  yeasts 
especially  for  household  purposes.  Cultivated  yeasts  are 
simply  wild  yeasts  from  the  air  which  have  been  freed 
from  impurities  and  planted  in  some  pure  food  material, 
where  they  grow  in  abundance,  giving  finally  a  mass 
of  pure  yeast.  Cultivated  yeasts  are  now  used  almost 
universally  by  all  bread  makers  because  of  their  greater 
reliability. 

FERMENTING  POWER  OF  DIFFERENT  YEASTS 

The  cultivated  yeast  used  to-day  in  bread  raising  has 
been  gradually  selected  from  a  large  variety  of  species. 
The  microscopist  recognizes  many  different  kinds  of 
yeasts,  varying  in  their  microscopic  appearance,  their 
rapidity  of  growth,  and  their  power  of  producing  fermen- 
tation, as  well  as  in  other  important  characteristics.  Most 


FERMENTING  POWER  OF  DIFFERENT  YEASTS     77 


of  them  will  raise  bread,  but  some  of  them  are  poorly 
adapted  to  this  purpose.  Some  of  them,  like  brewer's 
yeast,  act  so  slowly 
that  the  bread  will  not 
rise  rapidly  enough. 
The  use  of  yeast 
in  bread  making  is 
dependent  entirely 
upon  its  fermenta- 
tive power,  and  con- 
sequently the  value 
of  any  type  of  yeast 
will  depend  upon 
the  energy  of  its 
fermentation.  Some 
types  of  yeast  pro- 
duce a  more  vigor-  FIG.  38. 
ous  fermentation 
than  others.  The 
cake  of  compressed 
yeast,  for  example, 
produces  a  more  vig- 
or ous  fermentation 
in  bread  than  either  the  brewer's  yeast  or  the  dried  cake. 
The  relative  value  of  the  three  types  in  fermenting  flour 
is  shown  in  Fig.  38.  In  each  tube  was  placed  a  mixture 
of  flour  and  water  so  as  to  fill  completely  the  closed  arm 
on  the  right.  Each  was  then  inoculated  with  a  different 
yeast,  the  same  quantity  in  each.  As  they  fermented 
the  sugar  in  the  flour,  the  gas  given  off  collected  in  the 
closed  arm  as  shown,  and  the  vigor  of  the  fermentation 


Three  fermentation  tubes  inocu- 
lated with  different  varieties  of  yeast,  show- 
ing the  differences  in  fermenting  power,  as 
indicated  by  the  amount  of  gas  collected  in 
the  closed  tube.  The  tube  on  the  right  was 
inoculated  with  dried  yeast,  the  middle  tube 
with  brewer's  yeast,  and  the  left-hand  tube 
with  compressed  or  distillery  yeast. 


78  BACTERIA,  YEASTS,  AND   MOLDS 

may  be  inferred  from  the  amount  of  gas  produced.  It  will 
be  seen  that  the  tube  on  the  left  has  in  the  inclosed  arm 
a  much  larger  amount  of  gas  than  is  found  in  either  of 
the  other  samples.  This  tube  was  inoculated  with  a  dis- 
tillery yeast  (compressed  yeast),  and  the  experiment  shows 
that  this  type  of  yeast  has  a  greater  fermentative  power 
upon  flour  than  either  of  the  other  two  forms.  It  sug- 
gests also  that  this  yeast  will  be  the  most  satisfactory 
for  the  ordinary  domestic  purpose  of  bread  raising. 

There  are  also  other  factors  concerned  in  the  choice  of 
a  proper  species  of  yeast.  Some  kinds  of  yeast  give  a 
sour  or  otherwise  unpleasant  taste  to  bread,  and  others 
give  to  the  bread  an  undesirable  color.  From  the  many 
varieties  of  yeast  which  might  be  used  for  this  purpose 
certain  ones  have  been  chosen  by  the  brewers  as  par- 
ticularly well  adapted  for  their  type  of  fermentation ; 
others  are  commonly  used  in  distilleries.  But  this  does 
not  necessarily  make  them  the  best  for  bread  raising.  A 
long  experience  in  baking  has  resulted  in  the  selection 
of  the  type  best  adapted  for  bread  raising,  and  this  is 
a  species  that  grows  quickly  in  dilute  sugar  solutions 
and  hence  raises  the  bread  in  a  few  hours.  At  the  same 
time  it  gives  rise  to  a  pleasant,  agreeable  taste,  and  pro- 
duces no  color.  Consideration  of  all  these  phenomena 
has  been  clearly  essential  in  selecting  a  yeast  which  is 
best  adapted  for  bread  making. 

All  of  the  yeasts  used  by  brewers  and  distilleries 
to-day  belong  to  the  same  species,  and  this  species  is  also 
the  best  for  bread  raising.  But  although  all  one  species 
there  are  several  quite  distinct  varieties  having  different 
fermenting  powers. 


DIFFERENT    KINDS   OF   YEAST  79 

DIFFERENT  KINDS  OF  COMMERCIAL  YEAST 
PREPARATIONS 

In  the  early  periods  of  bread  making  there  were  no 
means  of  obtaining  pure  yeast.  Gradually,  however,  we 
have  learned  to  cultivate  the  yeasts  by  themselves,  until 
at  the  present  time  there  are  quite  a  number  of  methods 
for  producing  tolerably  pure  masses  of  yeast.  The  chief 
preparations  of  this  sort  are  given  in  the  following  pages 
and  all  one  species,  known  as  Saccharomyces  cerevisice ;  but 
although  belonging  to  one  species  there  are  a  number  of 
varieties  differing  in  several  characters. 

Compressed  Yeast.  At  the  present  time  the  yeast  most 
commonly  used  by  the  housekeeper  is  the  compressed 
yeast  cake.  This  well-known  commercial  article  consists 
of  a  soft,  somewhat  soggy  material,  composed  of  large 
quantities  of  yeast  plants  mixed  together  with  a  certain 
amount  of  starch  and  a  varying  quantity  of  other  material. 
This  yeast  is  originally  a  distillery  yeast,  which  the  manu- 
facturers of  certain  alcohol  products  sow  in  large  vats 
containing  materials  upon  which  the  plant  feeds  readily. 
The  yeast  grows  vigorously  and  after  a  time  collects  as  a 
scum  on  the  surface  of  the  vat.  This  is  removed,  washed, 
and  the  water  partly  removed ;  then  the  mass  is  pressed 
into  cakes  and  sold  to  the  public. 

This  compressed  yeast  is  the  most  convenient  and  reli- 
able type  of  yeast  culture  that  has  been  produced.  In 
the  fresh  cake  nearly  all  of  the  yeast  plants  are  alive  and 
vigorous,  and  the  results  obtained  from  their  use  are  almost 
uniformly  satisfactory.  Compressed  yeast  has  one  disad- 
vantage :  it  will  not  keep  long,  and  hence  must  be  used 


80  BACTERIA,   YEASTS,  AND    MOLDS 

while  fresh  or  the  proper  results  will  be  lacking.  If  the 
yeast  cake  is  kept  for  a  day  or  two  only,  the  plants  begin 
to  die,  and  after  three  or  four  days  only  a  small  number 
of  them  may  be  left  alive.  Such  yeast  when  a  few  days 
old  will  not  produce  as  quick  a  raising  of  the  bread  as 
the  fresh  cake.  More  than  this,  a  result  is  frequently 
experienced  in  old  cakes  that  is  worse  than  the  loss  of 
activity.  The  commercial  compressed  yeast  is  never  a 
pure  yeast,  but  contains  a  variety  of  other  microscopic 
plants,  among  which  are  bacteria  as  well  as  other  yeasts. 
These  other  organisms  are  liable  to  grow  in  the  cake  if 
kept  for  a  few  days.  The  yeast  may  even  decay,  which 
indicates  an  excessive  growth  of  bacteria ;  but  if  it  does 
not  decay  it  is  quite  certain  that  in  an  old  cake  other 
kinds  of  yeast  or  bacteria  are  relatively  more  abundant 
than  they  are  in  the  fresh  cake.  When  such  an  old 
yeast  cake  is  used  it  may  give  rise  to  undesirable  fermen- 
tations in  the  bread,  resulting  in  unpleasant  flavors.  If 
it  is  necessary  to  keep  a  compressed  yeast  cake  some 
days  before  using  it,  it  is  best  preserved  by  placing  it 
in  cold  water  and  keeping  it  in  an  ice  chest,  but  it  should 
never  be  allowed  to  freeze. 

Where  the  compressed  yeast  cake  can  be  obtained  fresh, 
however,  it  is  the  most  convenient  form  in  use.  It  is  so 
cheap  that  the  expense  need  not  be  considered  in  the 
household,  where  only  a  small  amount  is  needed.  But 
where  large  quantities  of  bread  are  to  be  made,  com- 
pressed yeast  is  somewhat  expensive,  and  it  is  cheaper 
then  to  brew  one's  own  yeast.  Consequently  bakers 
long  adhered  to  their  own  methods  of  making  yeast,  to 
be  referred  to  presently,  instead  of  depending  upon  the 


DIFFERENT   KINDS    OF   YEAST 


8l 


FIG.  39.     Yeast  from 
a  dried  yeast  cake. 


commercial  product.  For  the  ordinary  housekeeper  the 
bother  of  making  the  yeast  brew  is  so  great,  the  results  so 
unreliable,  and  the  expense  of  compressed  yeast  so  slight, 
that  the  latter  is  now  almost  universally 
used.  To-day  many  bakers  have  given 
up  making  their  own  yeast  brews  and 
depend  upon  compressed  yeast. 

Dried  Yeast.  A  second  type  of  com- 
mercial yeast  is  the  dried  yeast  cake. 
This  is  prepared  by  cultivating  yeast, 
mixing  the  product  with  certain  ingredients,  chiefly  starch, 
pressing  into  cakes,  and  then  drying  the  product  at  a  low 
heat.  The  drying  perhaps  injures  or  kills  some  of  the 
yeast  plants,  but  a  great  many  of  them  remain  uninjured, 
and  may  be  found  for  a  long  time  in  the  dried  yeast  cake, 
still  alive  and  capable  of  growing  if  placed  under  proper 
conditions  (Fig.  39).  In  order  that  they  may  begin  to 

grow  again  they  must  be  mois- 
tened, and  in  using  a  dried  yeast 
cake  it  is  best  to  soak  it  in 
warm  water  to  which  has  been 
added  a  small  amount  of  sugar. 
The  sugar  furnishes  food  for 
the  yeast  plants,  and  by  soak- 
ing them  in  warm  water  they 
are  soon  brought  to  a  con- 
dition of  growth,  so  that  when 
added  to  the  bread  dough  they  readily  enough  produce  a 
fermentation  (Fig.  40). 

The  dried  yeast  cakes  are  not  quite  so  convenient  to 
use  as  the  compressed,  but  a  little  experience  will  enable 


FIG.  40.     The  same  yeast  after  a 
few  hours'  growth. 


82  BACTERIA,   YEASTS,  AND   MOLDS 

any  one  to  obtain  good  results  with  them.  Their  great 
advantage  is  that  they  need  not  be  absolutely  fresh.  The 
cakes  may  be  preserved  for  many  weeks  or  even  months, 
and  their  powers  will  not  be  destroyed.  They  cannot 
decay  or  mold,  since  they  contain  no  water.  It  is  always 
well  to  remember,  in  using  them,  that  the  drying  of  the 
yeast  destroys  some  of  the  yeast  plants  and  in  time  kills 
them  all.  If  such  a  yeast  cake  is  examined  week  after 
week,  an  increasingly  smaller  number  of  living  yeast 
plants  will  be  found,  and  finally  they  will  all  disappear. 
The  fresher  the  cakes  are  the  better,  and  those  that  are 
very  old  are  useless.  But  in  spite  of  this  fact  these  dried 
yeast  cakes  may  be  kept  for  many  weeks,  and  for  persons 
who  have  not  a  ready  access  to  a  market  they  are  much 
more  convenient  than  the  compressed  cakes. 

Sometimes  yeast  is  prepared  in  the  form  of  a  dry  powder. 
It  is  not  a  very  common  form,  and  the  statements  made 
concerning  dried  yeast  cakes  will  apply  equally  well  to 
yeast  powder. 

Brewer's  Yeast.  Yeast  has  frequently  been  sold  in  a 
liquid  form  by  brewers  to  bakers,  to  be  used  in  raising 
bread.  Yeast  from  such  a  source  is  different  in  variety 
and  action  from  that  of  the  compressed  or  dried  yeast 
cake.  It  grows  in  the  brewer's  fermenting  vats,  either  as 
the  "top"  yeast  or  the  "bottom"  yeast.  The  former 
grows  as  a  scum  on  the  top  of  the  vat,  while  the  latter 
sinks  to  the  bottom,  the  former  alone  being  used  for  bread 
raising.  The  first  that  appears  on  the  surface  of  the  vat 
is  commonly  removed,  since  it  is  liable  to  be  filled  with 
dirt  and  harmful  bacteria.  The  flavor  of  bread  raised 
with  brewery  yeast  is  a  little  different  from  that  raised  by 


YEAST   BREWS  83 

other  kinds,  and  is  sometimes  slightly  bitter,  thus  explain- 
ing the  difference  sometimes  noticed  in  the  flavor  of  baker's 
and  homemade  bread.  This  type  of  yeast  does  not  pro- 
duce so  vigorous  a  form  of  fermentation  in  flour  as  com- 
pressed yeast,  and  is  less  satisfactory  in  a  household.  Its 
use  even  by  bakers  has  largely  ceased. 

Cultivation  of  Yeast  Brews.  When  one  is  near  a  mar- 
ket, by  far  the  most  convenient  method  of  obtaining  yeast 
for  bread  making  is  to  purchase  the  compressed  cake ; 
but  when  one  is  far  from  market  a  fresh  supply  is  not 
easily  obtained.  Moreover,  we  have  noticed  that  if  yeast 
is  needed  in  large  quantities  the  compressed  yeast  is  some- 
what expensive.  It  is  then  certainly  cheaper  and  may 
sometimes  be  more  convenient  to  brew  one's  own  yeast. 
Brewing  yeast  is  a  very  easy  process  if  one  will  exercise 
a  little  care. 

First  one  prepares  a  mixture  known  as  the  brew,  in 
which  the  yeast  will  grow  readily;  and  then  he  inoculates 
this  mixture  with  a  small  quantity  of  yeast  from  some 
good  source  and  allows  the  material  to  grow.  Many 
varieties  of  mixtures  are  in  use  for  the  development  of 
yeast.  Two  good  formulae  are  as  follows. 

(i)    i  lb.  potatoes  (2)    l/2  Ib.  of  malt 

l/2  oz.  hops  y2  oz.  of  hops 

i  gal.  water  i  gal.  of  water 

To  prepare  the  first  of  these  mixtures,  boil  the  potatoes 
and  remove  the  skins ;  boil  again  until  thoroughly  soft,  and 
then  mash  finely.  Meantime  the  hops  are  to  be  heated 
with  the  water  to  nearly  the  boiling  point  for  a  couple 
of  hours,  to  dissolve  the  hop  extract.  After  this  the 


84  BACTERIA,  YEASTS,  AND    MOLDS 

liquid  is  to  be  strained  and  mixed  with  the  mashed  pota- 
toes. It  is  well  to  boil  again  for  a  few  moments  to 
destroy  any  microscopic  organisms  (bacteria  or  molds) 
that  may  have  found  entrance  into  the  brew  during  its 
preparation.  The  material  is  then  to  be  cooled  and  may 
be  allowed  to  ferment  spontaneously.  But,  since  the 
results  are  then  unreliable,  there  is  usually  added  to  it, 
after  it  is  cooled  to  the  temperature  of  70°  to  80°,  a  small 
quantity  of  pure  yeast  from  some  reliable  source.  The 
whole  is  to  be  stirred  occasionally  and  allowed  to  stand 
until  the  yeast  has  developed  for  a  few  days.  The  yeast 
will  then  be  present  in  large  quantity  in  the  brew,  and 
can  be  used  for  any  desirable  purpose. 

In  making  the  second  of  the  above  brews,  the  process 
is  nearly  the  same.  The  hops  are  steamed  or  heated  with 
the  water,  as  in  the  first  case,  and  then  mixed  with  the 
malt  according  to  the  proportions  given  in  the  formula. 
The  subsequent  treatment  is  identical  in  both  cases. 

Some  such  method  of  preparing  yeast  was  in  former 
years  almost  universally  used  for  baking.  Brewing  yeast 
is  inexpensive,  simply  requiring  a  little  care  ;  but  with  the 
introduction  of  the  convenient  compressed  yeast  at  a  small 
price  this  method  of  making  yeast  has  practically  disap- 
peared from  the  household.  It  is  still  retained,  however, 
in  some  places  where  large  quantities  of  yeast  are  used. 

The  hops  are  added  to  these  brews,  not  as  food  for  the 
yeast,  but  for  two  other  purposes  :  (i)  They  give  a  slight 
nutty  flavor  which  is  subsequently  imparted  to  the  bread, 
somewhat  improving  its  taste.  (2)  The  extract  of  hops  is 
a  partial  antiseptic,  in  a  measure  preventing  the  growth  of 
bacteria,  though  not  injuriously  affecting  yeast.  Without 


YEAST   BREWS  85 

the  hops  various  mischievous  bacteria  would  be  almost 
sure  to  develop  in  the  brew,  injuring  or  perhaps  ruining 
it.  The  slimy-bread  bacterium,  for  example  (see  page  93), 
is  liable  to  grow  in  these  brews,  but  the  hop  extract  has  a 
decidedly  antiseptic  power  against  it. 

By  a  method  somewhat  similar  to  the  above,  breweries 
and  distilleries  cultivate  yeast ;  but  in  these  large  estab- 
lishments, where  there  is  a  demand  for  large  quantities  of 
yeast  of  the  highest  grade,  a  care  is  given  to  the  brewing 
impossible  in  the  home.  The  brewer  uses  a  microscope 
to  test  his  product,  and  exercises  a  care  in  cultivating  his 
yeast  which  insures  its  purity.  Yeast  from  such  sources 
is  therefore  more  reliable  than  any  other,  and  consequently 
most  yeast  in  use  to-day  comes  from  breweries  or  dis- 
tilleries, or  from  institutions  where  it  is  grown  upon  a 
large  scale.  Home  brewing  of  yeast  is  unreliable  and 
unsatisfactory. 


CHAPTER  VII 


BREAD   RAISING;    FERMENTED    LIQUORS 
WHAT  is  BREAD  RAISING? 

The  method  by  which  yeast  makes  bread  light  is  very 
simple  and  easily  understood.     There  is  present  in  the 

bread  dough,  at  the  start,  a 
small  amount  of  sugar  which 
comes  from  the  flour;  but 
there  is,  in  addition,  a  con- 
siderable quantity  of  starch, 
and  with  the  starch  there  is 
also  present  in  the  flour  a 
small  amount  of  a  material 
known  as  diastase.  By  the 
action  of  this  diastase  in 
the  dough,  part  of  the  starch 
is  converted  into  sugar. 
Thus  there  is  present  in 
the  dough,  after  it  is  mixed, 
a  sufficient  quantity  of  sugar 


FIG.  41.  Recently  mixed  dough  in- 
oculated with  yeast,  but  before 
the  yeast  has  grown. 


to  furnish  proper  ferment- 
able material  for  the  yeast. 

The  baker  mixes  the  fresh,  active  yeast  with  the  dough, 
and  places  the  whole  in  a  warm  place  where  the  yeast 
will  be  stimulated  into  active  growth  (Fig.  41). 

86 


WHAT   IS   BREAD   RAISING 


The  yeast  begins  to  feed  upon  the  materials  in  the 
dough  and  ferments  the  sugar,  producing  carbon  dioxide 
and  alcohol.  Both  of  these  materials  remain  for  a  while 
in  the  dough,  the  alcohol  dissolving  in  the  water,  and  the 
carbon  dioxide  accumulating  as  a  gas  in  small  bubbles. 
The  dough  is  so  sticky  and  heavy  that  it  is  not  possible 
for  these  bubbles  to  rise  up 
through  the  dough  as  it  does 
in  ordinary  fermented  liquids 
(Fig.  31).  The  gas,  there- 
fore, simply  collects  as  small 
bubbles  in  the  midst  of  the 
dough,  causing  the  dough 
to  swell.  This  is  the  so- 
called  raising  of  the  bread, 
and  the  bread  maker  must 
learn  from  experience  when 
it  has  progressed  suffi- 
ciently. After  the  dough 
has  been  properly  "  raised "  FlG.  42.  The  same  dough  after 

by    the     yeast,    it     may    be          yeast  has  grown  and  caused  the 

seen  to  be  filled  with  holes 
occupied  by  the  gas  bub- 
bles (Fig.  42).  Now,  after  the  proper  kneading,  it  is  put 
in  the  oven  for  baking.  The  heat  of  baking  drives  off 
the  small  amount  of  alcohol  which  is  contained  in  the 
bread.  The  heat  also  expands  the  bubbles  of  gas  so  as 
to  enlarge  the  little  holes  in  the  dough,  thus  causing 
it  to  swell  still  more ;  but  while  this  is  being  done 
the  heat  hardens  the  dough  into  the  firm  texture  of  the 
baked  bread,  and  the  holes  previously  occupied  by  the 


dough  to  swell  up  by  the  accumu- 
lation of  carbon  dioxide. 


88 


BACTERIA,   YEASTS,  AND    MOLDS 


carbon  dioxide  gas  are  left  as  pores  in  the  bread  (Fig.  43). 
This  makes  the  bread  light  and  porous,  and  gives  it  the 
character  that  every  one  is  familiar  with  in  properly  raised 
bread.  If  it  were  not  for  these  holes,  the  dough  would 
be  a  hard,  tough  mass,  difficult  to  bake  and  more  difficult 

to  digest. 

The   purposes    of   the 

raising  of  bread  by  yeast 

are  three. 

1.  It    makes    the    ma- 
terial   Lighter,    i.e.    more 
porous,  and  hence  easier 
of  mastication  and  more 
palatable. 

2.  It  renders  it  more  di- 
gestible, because  the  por- 
ous material  is  more  easily 

FIG.  43.  The  same  material  after  bak-  acted  Upon  by  the  digest- 
ing, showing  the  cavities  left  after  iye  jukes  than  the  mQre 
the  carbon  dioxide  is  expelled. 

solid  unleavened  bread. 

3.  The  yeast  imparts  a  certain  flavor  to  the  bread 
which  enhances  its  value.  This  flavor,  due  to  yeast,  is 
well  shown  by  the  difference  in  the  flavor  of  bread  raised 
in  the  ordinary  household  and  that  sometimes  raised  by 
bakers,  where  a  different  species  of  yeast  is  used. 

That  the  flavor  produced  -by  yeast  is  an  important 
factor  may  be  realized  also  by  comparing  the  flavor  of 
bread  raised  by  yeast  with  that  made  light  by  chemical 
or  mechanical  means.  Any  process  which  will  fill  the 
dough  with  bubbles  will  make  it  light.  In  one  type  of 
bread,  known  as  aerated  bread,  the  spaces  or  cavities  in 


*        '  *I 

""•? 

-*••-*.-  ;-& 


RELATION  OF  BREAD  RAISING  TO  TEMPERATURE    89 

the  dough  are  produced  by  mechanically  mixing  air  with 
the  dough.  The  result  is  a  bread  that  is  light  enough 
but  lacks  the  peculiar  flavor  present  in  ordinary  raised 
bread.  In  another  type  of  bread  (qtdck  biscuits]  chemical 
means  are  relied  upon  to  produce  the  gas.  A  small  quan- 
tity of  cream  of  tartar  and  saleratus  is  mixed  with  the 
dough.  These  two  materials  act  upon  each  other  chem- 
ically and  give  rise  to  a  quantity  of  carbon  dioxide  gas, 
which  appears  very  quickly,  and  rapidly  fills  the  dough 
with  bubbles  of  gas.  The  dough>  when  subsequently 
baked,  is  light,  but  has  a  flavor  quite  different  from  that 
which  would  be  produced  in  the  same  dough  if  it  were 
raised  by  the  action  of  yeast.  No  other  method  of  pro- 
ducing lightness  in  the  dough  gives  quite  so  good  flavors 
as  can  be  obtained  by  the  use  of  yeast,  and  none  is  thought 
to  make  bread  quite  so  easy  of  digestion. 

RELATION  TO  TEMPERATURE 

The  growth  of  yeast,  and  hence  the  raising  of  bread,  is 
very  closely  dependent  upon  temperature.  Yeasts  grow 
readily  in  warm  temperatures,  less  readily  in  low  tempera- 
tures, and  not  at  all  if  the  temperature  is  in  the  vicinity 
of  freezing.  Common  yeast  grows  best  if  kept  between 
75°  and  90°  F.  At  higher  temperatures  the  yeast  does 
not  produce  such  good  results,  since  certain  other  injurious 
microorganisms  (bacteria}  are  then  likely  to  grow.  If 
the  dough  is  kept  at  a  temperature  above  90°,  there  is 
almost  sure  to  be  trouble  from  the  growth  of  undesired 
organisms  which  give  rise  to  unpleasant  flavors.  Bread 
made  from  such  dough  is  very  apt  to  be  sour.  The 


90  BACTERIA,  YEASTS,  AND    MOLDS 

temperature  should  be  higher  in  winter  than  in  sum- 
mer, owing  partly  to  the  fact  that  flour  in  winter  is 
quite  sure  to  be  cold  and  to  require  some  time  to  become 
warm.  In  winter  a  temperature  of  95°  is  not  too  great 
for  the  proper  raising  of  the  dough,  while  in  summer  a 
temperature  of  70°  is  more  satisfactory.  In  the  raising 
of  bread  dough  it  is  always  far  better  to  use  a  ther- 
mometer and  to  determine  the  exact  temperature.  This 
is  rarely  done  in  the  ordinary  kitchen.  It  is  more  com- 
mon to  place  the  dough  near  the  stove  and  trust  that 
the  temperature  will  be  close  enough  to  that  desired. 
It  is  not  possible,  under  these  circumstances,  to  depend 
absolutely  upon  the  results.  In  the  majority  of  cases 
the  dough  is  fermented  satisfactorily,  but  bad  batches 
of  bread  from  this  cause  are  a  frequent  experience  of 
the  housewife.  To  produce  uniform  results  it  is  quite 
necessary  to  use  a  thermometer,  and  then  the  dough  may 
surely  be  kept  within  the  limits  of  temperature  above 
mentioned. 

The  length  of  time  for  yeast  to  grow  in  the  dough  before 
baking  is  dependent  upon  the  temperature  of  the  fermen- 
tation ;  but  it  is  important  that  it  should  not  be  too  long. 
If  the  temperature  is  low  (below  70°),  so  that  it  requires 
a  longer  time  than  usual  for  the  dough  to  rise  sufficiently, 
the  texture  of  the  bread  is  apt  to  be  crumbly  and  brittle, 
and  a  sour  taste  is  very  likely  to  develop,  due  to  the 
growth  of  other  microorganisms  besides  the  yeast.  If, 
on  the  other  hand,  the  bread  rises  too  quickly,  owing  to 
too  high  a  temperature,  an  abundance  of  gas  is  produced 
which  makes  the  dough  rise  rapidly;  but  the  bread  will 
be  inferior  in  flavor,  texture,  and  color.  The  best  results 


IMPURITIES    IN    COMMERCIAL   YEAST  91 

are  obtained  by  a  moderately  active  growth  of  the  yeast, 
which  will  produce  a  sufficient  amount  of  lightness  in  the 
dough  in  the  course  of  eight  or  ten  hours. 

IMPURITIES  IN  COMMERCIAL  YEAST 

One  factor  largely  determining  the  value  of  commercial 
yeast  is  its  purity.  It  rarely  or  never  happens  that  a 
yeast  cake,  or  yeast  culture  of  any  form,  is  composed 
purely  of  yeast.  There  is  almost  certain  to  be  mixed  with 
it  a  quantity  of  bacteria.  Frequently  there  is  also  pres- 
ent a  variety  of  mold  spores,  and  the  yeast  cake  is  also 
likely  to  contain  other  species  of  yeast  besides  the  one 
desired  for  bread  raising.  These  impurities  maybe  abun- 
dant or  scanty  in  any  cake  of  yeast.  If  they  are  present 
at  all,  they  may  produce  trouble,  but  this  will  depend  upon 
circumstances.  The  yeast  plants  themselves  are  present 
in  such  overwhelming  proportions  that,  under  ordinary  cir- 
cumstances, the  impurities  get  little  opportunity  to  develop. 
If  the  raising  is  conducted  at  a  proper  temperature,  the 
impurities  will  rarely  do  much  injury.  In  the  common 
use  of  yeast,  therefore,  in  spite  of  the  fact  that  various 
bacteria  and  mold  spores  may  be  mixed  with  the  dough 
when  the  yeast  is  added,  the  bread  rises  in  a  normal  way, 
and  the  impurities  produce  no  trouble. 

These  foreign  bacteria  in  the  yeast  cake  are  quite  sure 
to  increase  with  its  age.  While  the  yeast  plants  do  not 
multiply  in  the  compressed  yeast  cake,  the  bacteria  are 
almost  sure  to  do  so,  especially  if  the  cake  is  kept  in  a 
moist  condition  for  some  days  before  using.  An  old  yeast 
cake  is  therefore  quite  sure  to  contain  more  of  these 


92  BACTERIA,  YEASTS,  AND    MOLDS 

impurities  than  a  fresh  one.  Moreover,  in  an  old  cake, 
as  we  have  seen,  the  number  of  living  yeast  cells  is  less 
than  in  a  fresh  one,  and  so  the  undesirable  germs  have  a 
better  chance  to  grow  in  the  dough.  The  use  of  an  old 
yeast  cake  is  therefore  unwise,  since  the  bread  may  thus 
be  ruined.  The  fermentation  does  not  progress  rapidly 
enough,  the  bread  must  be  kept  longer  at  a  warm  tem- 
perature, and  during  this  whole  period  the  other  yeasts  or 
bacteria  have  a  chance  to  develop  and  produce  a  variety 
of  bad  flavors.  If  one  uses  fresh  yeast  cakes,  there  is  little 
probability  that  any  trouble  will  arise  from  the  action  of  the 
smaller  number  of  bacteria  or  molds  that  may  be  present. 
Sour  Bread.  The  impurities  from  the  yeast  or  from 
some  other  source  do,  however,  occasionally  produce 
trouble,  two  types  of  which  are  so  common  as  to  demand 
notice.  The  raising  of  dough  by  means  of  yeast  some- 
times causes  it  to  become  sour.  The  dough  rises  in  the 
proper  manner  apparently,  but  the  bread  when  baked  is 
found  to  have  an  unpleasant,  sour  taste.  This  is  espe- 
cially likely  to  happen  if  the  bread  is  raised  too  long. 
By  some  this  sour  taste  is  regarded  as  an  improvement  to 
the  flavor.  It  is  due  to  the  development,  during  the  fer- 
mentation, of  certain  acids  in  the  dough,  which  come,  not 
from  the  action  of  yeasts,  but  from  the  growth  of  bacteria 
that  are  present  either  in  the  yeast  or  flour.  It  has  been 
a  disputed  question  whether  the  acid  produced  is  lac- 
tic, acetic,  or  butyric.  (Lactic  acid  is  like  that  formed  in 
sour  milk,  acetic  acid  is  formed  in  vinegar,  and  butyric 
acid  is  the  acid  found  in  old  rancid  butter.)  It  is  fre- 
quently a  mixture  of  all  three,  but  ordinarily  it  is  prob- 
ably mostly  lactic  acid.  Each  of  these  acids  is  known 


SOUR  BREAD  93 

to  be  produced  by  bacteria.  Since  the  acids  are  caused 
by  bacteria,  this  subject  really  belongs  to  a  later  division 
of  our  discussion  ;  but  its  close  relation  to  bread  making 
leads  to  its  introduction  at  this  point. 

Recognizing  that  the  cause  of  sour  bread  is  due  to 
the  growth  of  bacteria,  it  is  not  difficult  to  suggest  the 
proper  means  of  avoiding  it.  Fresh  yeasts  only  should 
be  employed.  A  good  quality  of  flour  should  be  used,  and 
the  dough  should  be  mixed  in  clean  utensils.  After  mix- 
ing, the  dough  should  be  placed  in  a  clean  dish  at  a  proper 
temperature  (75°  in  summer,  90°  in  winter),  so  that  the 
bread  will  rise  in  about  eight  hours.  Dough  should  never 
be  allowed  to  ferment  too  long.  Strict  attention  to  these 
details  will  commonly  remove  the  trouble. 

The  bacteria  which  produce  sour  bread  do  not,  however, 
come  wholly  from  the  use  of  impure  yeasts,  for  the  flour 
itself  is  likely  to  contain  some  organisms  which  may  cause 
this  trouble.  A  sour  taste  is  much  more  likely  to  be 
found  in  bread  made  from  poor  grades  of  flour  than  in 
that  made  from  the  higher  grades.  This  is  perhaps  due 
to  the  fact  that,  owing  to  difference  in  the  method  of 
manufacture,  the  lower  grades  of  flour  contain  a  larger 
number  of  bacteria.  The  same  trouble  is  also  sometimes 
caused  by  the  use  of  unclean  utensils  in  the  mixing  of  the 
dough,  or  by  leaving  the  dough  to  rise  in  a  dish  not  thor- 
oughly washed.  Unclean  utensils  are  sure  to  have  a  large 
number  of  bacteria  attached  to  them,  and  these  bacteria, 
becoming  mixed  with  the  dough,  grow  there  readily  side 
by  side  with  the  yeast. 

Slimy  Bread.  In  recent  years  it  has  been  noticed  that, 
a  few  hours  after  baking,  bread  sometimes  becomes  slimy. 


94        BACTERIA,  YEASTS,  AND  MOLDS 

When  perfectly  fresh  it  does  not  show  any  sliminess,  but 
after  standing  a  few  hours  the  inside  of  the  loaf  appears 
more  or  less  moist,  and  shows  a  slimy  texture  when  broken, 
looking  as  if  permeated  with  cobwebs.  This  trouble  is 
occasionally  met  with  in  the  household,  but  more  commonly 
in  bakeries.  Indeed,  sometimes  sliminess  has  become  so 
troublesome  in  certain  bake  shops  as  nearly  to  ruin  the 
business,  the  trouble  reappearing  day  after  day  and  prov- 
ing extremely  difficult  to  remedy. 

The  cause  of  the  trouble  is  known  to  be  the  develop- 
ment of  certain  bacteria,  one  species  of  which  is  shown  in 
Fig.  44.    These  bacteria  are  capable 
of  growing  in  the  dough,  and  are 
not  killed  during  the  baking.    After 
the  bread  is  removed  from  the  oven 
they  begin  a  rapid  growth,  if  the 
bread  is  kept  warm,  and  in  a  few 
hours  produce  the  trouble  de- 
FIG.  44.    A  species  of  bac-    scribed      These  bacteria  frequently 

tenum    which    produces  * 

slimy  bread.  come  from  the  yeast,  but  in  some 

cases,  where  the  subject  has  been 

studied  in  detail,  it  has  appeared  that  the  source  is  the 
flour  rather  than  the  yeast.  Certain  samples  of  flour  con- 
tain these  mischievous  organisms,  and  when  bread  is  made 
from  such  flour  it  is  difficult  to  avoid  their  presence  and 
growth.  A  change  to  a  new  brand  of  flour  will  then 
obviate  the  trouble.  If  a  housewife  should  experience 
this  slimy  bread  fermentation,  the  proper  method  of  pro- 
cedure is  (i)  to  use  a  new  brand  of  flour  for  bread  mak- 
ing, (2)  to  sterilize,  by  methods  to  be  referred  to  later, 
all  utensils  that  are  used  in  connection  with  bread  making, 


ALCOHOL  AND   CARBON   DIOXIDE  95 

and  (3)  to  get  a  fresh  supply  of  yeast.  After  this  the 
trouble  ought  to  disappear.  It  is  also  important  to 
remember  that  the  sliminess  only  occurs  if  the  bread  is 
kept  warm,  and  hence  chiefly  in  the  summer.  If  the 
bread  is  cooled  at  once  and  kept  in  a  cool  place  until  it  is 
eaten,  the  trouble  is  not  likely  to  manifest  itself  even 
though  the  slimy  bacteria  are  present.  The  bread  is 
wholesome  enough  even  though  slimy. 

THE  UTILIZATION  OF  BOTH  ALCOHOL  AND  CARBON 
DIOXIDE 

In  the  immense  fermentation  industries  involving  the 
production  of  beers,  porters,  ales,  etc.,  both  of  the  products 
of  fermentation  are  commonly  utilized.  The  general  char- 
acter and  effect  of  beer  are  due  partly  to  the  alcohol  pres- 
ent and  partly  to  the  presence  of  a  quantity  of  the  car- 
bon dioxide,  which  gives  to  the  beer  its  sparkle.  In  the 
manufacture  of  such  a  product  the  fermentable  material, 
usually  some  form  of  grain,  is  inoculated  with  a  large 
quantity  of  a  vigorous  yeast,  a  species  being  chosen  that 
has  been  found  by  experience  to  produce  the  desired 
results.  A  fermentation  starts  up  which  progresses  rap- 
idly if  the  temperature  is  kept  warm,  as  it  is  in  the  man- 
ufacture of  common  beer.  The  fermentation  lasts  a  few 
days.  If  the  temperature  is  low,  as  in  the  production  of 
the  so-called  lager  beer,  the  fermentation  lasts  many  weeks. 
During  this  fermentation  alcohol  accumulates  in  the  liquid, 
and  the  carbon  dioxide  gas  escapes  into  the  air,  forming 
a  froth  in  the  fermenting  vat.  The  yeast  increases  in 
amount,  and  either  collects  on  the  surface  or  sinks  to 


96  BACTERIA,  YEASTS,  AND   MOLDS 

the  bottom.  Most  of  the  yeast  is  then  removed,  and 
the  liquid  stored  in  casks  or  bottles.  Here  the  fermen- 
tation continues  for  a  time,  but  rather  slowly.  Since  the 
vessels  are  closed  the  carbon  dioxide  gas  cannot  escape, 
but,  accumulating  in  the  vessel,  is  partly  dissolved  in  the 
liquid  itself.  The  gas  exerts  considerable  pressure  inside 
the  bottle  or  cask,  and  when  it  is  opened  the  expansion 
of  the  gas  gives  rise  to  the  popping  of  the  corks  and  the 
bubbling  and  frothing  of  the  beer ;  in  other  words,  to  the 
sparkle.  Beers  are  usually  drunken  while  they  are  toler- 
ably fresh,  and  sometimes  before  fermentation  has  wholly 
ceased,  though  some  types  of  beer  are  kept  for  months. 
In  all  such  fermented  products  the  carbon  dioxide  is 
desired  no  less  than  the  alcohol,  since  it  contributes 
materially  to  the  flavor  of  the  product.  In  the  production 
of  sparkling  wines  a  similar  effect  is  produced  by  a  sec- 
ondary fermentation,  forming  carbon  dioxide  in  the  wine 
after  it  is  placed  in  the  bottles  (Fig.  45,  b). 

For  those  interested  simply  in  home  problems  the  fer- 
mentation of  beers  is  of  little  importance.  It  is  carried 
on  chiefly  in  the  great  breweries,  where  beer  is  made  on  a 
large  scale,  but  only  to  a  very  limited  extent  in  the  house- 
hold itself.  It  has  been,  however,  a  somewhat  common 
procedure  in  certain  households  to  make  homemade  beer 
on  a  small  scale.  In  previous  years  this  was  made  from 
certain  roots  and  extracts  of  strongly  flavored  plants. 
For  example :  home  beers  have  been  made  from  a  mixture 
of  molasses  and  hops  flavored  with  spruce  extract ;  or 
sugar  and  ginger  with  lemon  for  flavor ;  or  a  mixture  of 
sugar,  crushed  raisins,  and  lemon;  but  to-day  highly 
flavored  extracts  are  purchasable  at  stores  for  a  small 


BREAD    RAISING;    FERMENTED    LIQUORS         97 


price.  These  flavoring  extracts  are  mixed  at  home  with 
a  quantity  of  sugar  and  water  (two  pounds  sugar  to  ten 
quarts  water).  To  the  mixture  is  added  a  considerable 
amount  of  yeast  (one  cake  for  the  above  quantity),  and  the 
whole  material,  closed  in  bottles  or  other  vessels,  is  then 
set  aside  in  a 
warm  place  for 
fermentation. 
The  fermenta- 
tion goes  on 
rapidly,  and  in 
the  course  of  a 
couple  of  days 
a  beverage  is 
produced,  rilled 
with  carbon  di- 
oxide, which 
causes  a  bub- 
bling and  froth- 
ing when  the 
vessel  is  opened, 

and    containing  FIG.  45.     Miscellaneous  species  of  yeast. 

a  Small  quantity  a,  S.  cerevisice;  b,  S.  pastorianus  /,  from  wine;  c,  S.  pastoria- 
c     i       i-i        T>I_  nus  HI >  d>  S-  ellipsoideus  II;  e,  S.  cerevisice,  from  beer; 

of  alcohol.    The       ^  s  apiculatus. ^  s.  minor, 
amount  of  alco- 
hol in  such  beverages  is  small  if  the  fermentation  is  not 
kept  up  too  long ;  but  in  old  homemade  beer  the  alcohol 
may  be  considerable. 

Such  home-brewed  beer  has  come  to  be  somewhat 
extensively  used  in  recent  years.  In  its  manufacture  it 
must  be  remembered  that  the  fermentation,  which  results 


98        BACTERIA,  YEASTS,  AND  MOLDS 

in  the  production  of  carbon  dioxide  and  alcohol,  is  due  to 
the  action  of  the  yeast  upon  the  sugar  and  not  to  the 
beer  extract.  The  extract  is  added  in  these  cases  chiefly 
to  produce  a  peculiar  flavor  in  the  product,  which  renders 
it  palatable.  The  commercial  beer  extracts  simply  give  a 
pungent  taste  and  perhaps  stimulate  the  growth  of  the 
yeast ;  but  it  is  the  fermentation  of  the  sugar  that  causes 
the  sparkle  due  to  the  carbon  dioxide,  and  any  sugary 
solution  will  ferment  in  a  similar  way  if  yeast  is  added. 
The  product  is  not  palatable,  however,  unless  something 
is  present  to  give  it  a  flavor.  The  only  reason  why  such 
homemade  beers  are  less  intoxicating  than  commercial 
beers  is  because  the  fermentation  is  allowed  to  continue 
but  a  short  time,  long  enough  to  produce  an  abundance 
of  carbon  dioxide  but  only  a  little  alcohol. 

Fermented  Milk.  A  mild  fermented  beverage  is  occa- 
sionally made  from  milk  by  means  of  a  yeast.  It  is  called 
kumiss,  and  is  regarded  as  useful  for  invalids,  since  it 
is  supposed  to  be  more  easy  of  digestion  than  raw  milk. 
Its  preparation  is  as  follows.  Into  a  quantity  of  milk  is 
placed  a  little  common  sugar,  —  from  four  to  eight  table- 
spoonfuls  to  a  gallon  of  milk, — and  yeast  is  added  just  as  in 
homemade  beer,  one  fourth  of  a  cake  of  compressed  yeast 
in  a  little  water  being  sufficient  for  a  gallon  of  milk.  The 
mixture  is  put  in  a  warm  place  and  fermentation  sets  in. 
After  twenty-four  hours'  fermentation  the  material  is 
bottled  and  placed  on  ice ;  when  cool  it  is  ready  for  use. 
The  milk  becomes  slightly  soured,  giving  a  taste  much 
relished  by  some  people.  It  is  filled  with  carbonic  diox- 
ide and  contains  a  small  amount  of  alcohol,  and  is  thus  a 
sort  of  beer  made  from  milk.  It  is  not  much  used  in  this 


BREAD    RAISING;    FERMENTED   LIQUORS         99 

country  except  for  invalids.  Other  types  of  fermented 
beverages,  kefir,  mazoon,  and  some  others,  are  made  from 
milk  by  the  use  of  special  ferments,  always  containing 
yeast,  but  whose  preparation  is  hardly  within  the  reach 
of  the  ordinary  household. 


SECTION    III  — BACTERIA 


CHAPTER   VIII 
THE    GENERAL   NATURE    OF    BACTERIA 

Our  study  of  bacteria  must  be  more  extended  than  that 
which  we  have  given  to  either  molds  or  yeasts.  While 
molds  and  yeasts  are  of  significance  in  the  household,  the 
action  of  bacteria  is  much  more  fundamental  and  universal. 

i/  Bacteria  are  far  smaller 
than  yeasts  or  molds 
(Fig.  46).  They  are  com- 
monly unknown  to  the 
housewife  even  by  name, 
and  rarely  does  she  under- 
stand that  they  have  any 

FIG.  46.     Showing  the  comparative  size    relation    to    household 
of  molds  (a),  yeast  (b  and  c],  and  bac- 
teria (d)  economy,  or  concern    her 

very  closely.      Few   have 

ever  seen  them  or  been  aware  of  their  existence.  Never- 
theless they  are  so  constantly  at  work  upon  all  kinds  of 
food  products  in  the  pantry,  that  the  affairs  of  the  house- 
hold are  in  a  state  of  more  or  less  constant  warfare  against 
these  invisible,  unrecognized,  and  unknown  foes.  They 
are  more  serious  enemies  than  molds  or  yeasts.  Chiefly 
to  their  presence  and  activity  is  due  the  fact  that  the 
preservation  of  foods,  even  for  a  few  days,  is  frequently 

100 


STRUCTURE   OF   BACTERIA  IOI 

difficult,  while  special  devices  are   required  to  preserve 
food  indefinitely. 

To  the  housewife  bacteria  are  of  little  value  and  are 
foes,  like  the  molds,  rather  than  allies,  like  the  yeasts. 
This  does  not  mean  that  they  have  no  utility.     On  the 
contrary,  they  are  of  the  most  fundamental  importance  in 
nature,  and  it  is  no  exaggeration  to  say  that  the  very  con- 
tinuation of  life  is  dependent  upon  their  activity.     To  the 
agriculturist 
they  are  abso- 
lutely essen- 
tial.     They 
are  the  dairy- 
man's   close      FIG.  47.     Comparative  size  of  the  point  of  the  finest 
allies      and          cambric  needle  (£),  a  particle  of  dust  (a),  and  bac- 
teria (c). 

they  are  in- 
dispensable friends  of  many  industries.  By  their  action 
are  produced  some  of  the  articles  for  our  tables  (vinegar) 
and  also  the  flavor  of  butter  and  cheese.  However,  these 
phenomena  do-  not  directly  concern  the  housewife,  and, 
with  a  few  individual  exceptions,  bacteria  are  her  foes. 

STRUCTURE  OF  BACTERIA 

Size.  Bacteria  are  much  smaller  than  yeasts,  and  only 
the  high  powers  of  the  microscope  can  disclose  their 
presence  (Fig.  47).  Many  are  not  more  than  a  fifty 
thousandth  of  an  inch  in  diameter,  and  even  the  larger 
ones  are  not  much  more  than  a  ten  thousandth  of  an 
inch.  But  bacteria  are  far  more  abundant  in  nature  than 
yeasts.  They  are  present  in  great  numbers  in  the  earth, 


102  BACTERIA,   YEASTS,  AND   MOLDS 

the  air,  and  the  water,  and  are  sure  to  find  their  way  into 
every  kind  of  food  or  anything  else  that  may  be  exposed 
to  the  air.  They  are  also  much  more  troublesome  than 
molds  for  two  reasons  :  (i)  they  multiply  with  a  rapidity 
that  is  quite  inconceivable;  (2)  they  are  quite  invisible 
to  the  naked  eye,  and  their  presence  is  not  suspected 
until  they  become  numerous  enough  to  produce  undesired 
changes  in  the  material  upon  which  they  are  growing. 
As  a  result  they  present  a  vast  number  of  problems  to 
the  housewife,  which  she  has  dimly  seen  for  years,  but 
for  which  science  has  only  in  the  last  few  years  begun  to 
offer  solutions.  They  are  much  more  difficult  to  handle 
than  either  molds  or  yeasts,  because  they  are  smaller, 
more  numerous,  and  more  vigorous,  and  for  these  reasons 
it  is  almost  impossible  to  exterminate  them.  It  is  an 
impossibility  to  free  a  pantry  from  bacteria  and  very  diffi- 
cult to  guard  food  from  their  action. 

Shape.  Bacteria  are  very  simple,  and  there  are  such 
slight  differences  between  the  various  kinds  that  in  many 
cases  it  is  quite  impossible  by  microscopic  study  to  dis- 
tinguish one  species  from  another.  The  bacteriologist 
knows  to-day  that  many  bacteria  which  when  studied  under 
the  microscope  appear  absolutely  identical,  are  totally 
unlike  in  their  general  characters.  It  frequently  happens 
that  perfectly  harmless  bacteria  cannot  by  ordinary  micro- 
scopic study  be  distinguished  from  those  that  are  very  harm- 
ful. For  example,  the  bacillus  which  produces  typhoid  fever 
cannot  be  distinguished  microscopically  from  another  com- 
mon but  harmless  species  found  in  water.  For  this  reason 
the  microscopic  study  of  these  plants  gives  only  a  small 
part  of  the  facts  that  we  need  to  know  in  regard  to  them. 


CLASSIFICATION   OF   BACTERIA  103 

Classification.  A  consideration  of  the  classification  of 
bacteria  is  quite  unnecessary  for  the  purpose  of  our  work, 
inasmuch  as  they  are  so  minute  that  no  one  without  the 
aid  of  a  powerful  microscope  will  ever  be  likely  to  see 
these  organisms.  Their  activities  are  seen  on  all  sides, 
but  the  organisms  themselves  are  totally  below  the  reach 
of  our  vision.  It  is  sufficient,  therefore,  to  give  a  few 
facts  concerning  their  general  appearance. 

Bacteria  are  the  simplest  organisms  known.  They  are 
far  simpler  than  molds  and  even  simpler  than  yeasts.  So 
minute  are  they,  and  so  simple  in  their  structure,  that 
very  little  is  known  in  regard  to  them  at  the  present  time 
except  their  general  external  appearance.  They  are  uni- 
versally regarded  as  plants,  although  many  of  them  are 
endowed  with  a  power  of  motion  and  for  this  reason  might 
readily  be  mistaken  for  animals.  Biologists  have  learned, 
however,  that  many  plants  can  move,  and  they  are  univer- 
sally agreed  that  bacteria  must  be  classed  with  plants 
rather  than  animals. 

Flagella.  The  fact  that  many  bacteria  are  endowed 
with  the  power  of  motion  suggests  that  they  must  have 
locomotive  organs,  and  these,  indeed,  are  easily  seen  by 
proper  microscopic  study.  They  consist  of  minute  hairs 
which  project  from  the  body  of  the  bacteria.  Sometimes 
there  is  a  single  one  from  one  end,  sometimes  they  occur 
in  tufts,  and  occasionally  they  may  be  scattered  all  over 
the  bodies  of  the  bacteria  as  shown  in  Fig.  48.  These 
little  hairs  are  capable  of  waving  to  and  fro,  and  by  this 
motion  they  drive  the  bacteria  through  the  water.  Not 
all  bacteria  possess  such  locomotive  organs,  and  one 
means  by  which  scientists  classify  these  organisms  is  by 


104 


BACTERIA,  YEASTS,  AND    MOLDS 


the    presence   or   absence   of   these  motor   hairs.     They 

are  known  by  the  name  of  flagella. 

Spherical  Bacteria:  Cocci. 
The  simplest  type  of  bac- 
teria consists  of  those  that 
are  in  the  shape  of  a  minute 
sphere.  Their  size  differs 
somewhat,  but  they  are 
always  extremely  minute,  and 
about  all  that  can  be  said  in 
regard  to  them  is  that  they 
are  spherical  organisms, 
sometimes  possessing  flagella 
and  sometimes  apparently 

FIG.  48.    Cocci,  bacilli,  and  bac-  without   them.     No  internal 
teria.    a  (Coccus),  b  and  c  (Badi-  structure    is   known.      They 

/us),  show  flagella  ;  d(Bacterium)   multiply    sometimes    in    SUCh 


**» 


has  no  flagella. 


a   way  as     Q  OQ 
° 


to    produce    long    chains    (Fig.  49,  a), 

sometimes  so  as  to  produce  groups  of  a( 

fours    or   groups    of    eight    or   sixteen  ^^ 

(Fig.  49,  b,  c,  d).     The  general   name  fcp 

given  to  spherical  bacteria  is  coccus,  and 

to   this   name  are   sometimes    prefixed  FlG" 49'  Cocci>show- 

ing  methods  of  mul- 

certam  other  syllables  to  indicate  certain  tiplication.  a,  strep- 
characters.  Streptococcus  is  a  name  tococcus;  b,  Micro- 
given  to  cocci  forming  chains  (Fig.  49, 
a),  and  Micrococcns  to  those  forming 
fours  or  irregular  masses  as  at  b.  The  term  Sarcina  is 
the  name  given  to  those  that  form  solid  masses  such  as 
shown  in  Fig.  49,  c  and  d. 


coccus;     c    and 
Sarcina. 


CLASSIFICATION    OF   BACTERIA 


105 


Rod-shaped  bac- 
teria. 


Rod-shaped  Bacteria.  These  are  in  the  shape  of  rods 
of  greater  or  less  length.  They  are  usually  somewhat 
rounded  at  the  ends  and  may  be  only  a  little  longer  than 
they  are  broad,  or  they  may  be  Q 
very  many  times  as  long  as  broad 
(Fig.  50).  When  one  of  these  grows 
it  lengthens  and  commonly  soon 
divides  into  two,  but  they  may  con- 
tinue to  lengthen  for  a  time  without  FIG.  50. 
manifesting  any  signs  of  division. 
In  such  a  case  they  form  long  slender  threads,  as  shown 
in  Fig.  50,  b.  These  threads,  however,  eventually  break 
up -into  short  sections  (Fig.  50,  c).  Some  of  these  rod- 
shaped  bacteria  have  flagella  and  are  capable  of  active 
motion,  in  which  case  they  form  the  species  of  Bacillus 
(Fig  48,  c) ;  others  have  no  flagella  and  are  quite  with- 
out the  power  of  motion,  in  which  case  they  constitute  the 
species  Bacterium  (Fig.  48,  d). 

Spiral  Bacteria.  A  third  type  of  bacteria  is  in  the  form 
of  a  spiral  rod,  shown  in  Fig.  51.  These,  however,  are 
somewhat  uncommon  and  of  less 
importance  than  the  others.  Like 
the  other  forms  they  may  possess 
flagella  or  they  may  be  without 
them. 

Multiplication.  The  growth  and 
multiplication  of  bacteria  is  ex- 
tremely simple  and  consists  in  a 
lengthening  of  the  individual  followed  by  its  division.  A 
sphere  becomes  slightly  oval  in  shape  and  then  divides  in 
the  middle  to  produce  two  spheres,  as  shown  in  Fig.  52,  a. 


FIG.  51.     Spiral  bacteria. 


io6 


BACTERIA,  YEASTS,  AND  MOLDS 


OOCDOO 


One  of  the  rod-shaped  forms  lengthens  itself  and  divides 
in  the  middle  and  produces  two  individuals,  each  of  which 
again  lengthens  and  divides  (Fig.  52,  b).  The  same  method 
is  found  in  the  spiral  bacteria.  This  manner  of  division, 
which  is  characteristic  of  all  bacteria,  will  be  seen  to  be 
quite  different  from  the  method  we  have  already  noticed 
in  the  yeasts.  Indeed,  the  distinction  between  yeasts  and 
bacteria  is  based  upon  this  method  of  multiplication.  The 

method  of  multi- 
plication in  bac- 
teria is  known  as 
fission,  and  this 
group  of  fungi  are 
called  fission  fungi 
in  distinction 
from  the  yeasts, 
which  are  called 
budding  fungi.  The 
difference  between 
these  two  classes 
can  be  distin- 


FIG.  52.  Showing  the  method  of  multiplication 
by  fission,  a,  a  coccus  form  ;  6,  a  short  rod  ; 
c,  d,  and  e,  showing  the  method  of  growth  into 
long  chains  and  the  consequent  breaking  into 
sections. 


guished  only  by  careful  microscopic  study,  but  it  is  the 
scientific  distinction  between  the  two  groups. 

Spore  Formation.  Under  some  circumstances  bacteria 
have  a  different  method  of  multiplication.  Inside  of  the 
body  of  a  single  individual  bacterium  appears  a  little 
rounded  mass  which  is  known  as  a  spore  (Fig.  53).  This 
spore  may  be  broader  than  the  rod  which  produced  it, 
or  it  may  be  narrower  ;  but  it  finally  breaks  out,  the 
bacterium  itself  disappearing  and  the  spore  then  coming 
out  freely  in  the  medium  in  which  it  lives.  These 


GROWTH    OF   BACTERIA 


107 


spores  are  capable  of  subsequently  germinating  into 
new  individuals  like  those  that  produced  them  and  thus 
continuing  the  race  (Fig.  53,  b}. 

Not  all  bacteria  produce  spores,  and  the  question 
whether  any  species  of  bacteria  forms  spores  is  a  matter 
of  most  extreme  significance  in  connection  with  its  func- 
tions ;  for  these  spores  are  covered  by  a  little  shell  which 
is  hard  and  tough  and  capable  of 
resisting  various  adverse  condi- 
tions. Spore-bearing  bacteria 
may  be  dried  without  injury,  for 
their  spores  protect  them  from 
destruction.  They  may  be  heated 
to  a  high  temperature,  even  to 
boiling,  without  being  killed. 
Thus  the  presence  of  spores  will 
make  a  great  difference  in  the 
ease  with  which  any  material  can 
be  sterilized  by  heat.  Bacteria 


FIG.  53.  Showing  the  forma- 
tion of  spores.  At  a  is  a 
free  spore  and  at  b  a  germi- 
nating spore. 


not  capable  of  producing  spores  are  very  easily  killed  by 
heat,  while  the  spore-bearing  forms  are  destroyed  with 
much  greater  difficulty. 


GROWTH  OF  BACTERIA 

Rapidity  of  Growth.  The  most  striking  fact  in  regard 
to  bacteria  is  their  wonderful  rapidity  of  multiplication ; 
for  upon  this  are  dependent  their  extraordinary  powers. 
Bacteria  growth  and  multiplication  mean  the  same  thing, 
and  the  rapidity  with  which  they  can  multiply  is  almost 
inconceivable.  Certain  kinds  of  common  bacteria  can 


108  BACTERIA,  YEASTS  AND   MOLDS 

reproduce  themselves  once  every  half  hour,  the  result  of 
which  is  that  a  single  bacterium  will  have  become  two  in 
a  half  hour,  four  in  an  hour,  eight  in  an  hour  and  a  half, 
and  so  on.  This  increase  of  progeny  by  geometrical  pro- 
gression results  in  the  production  of  descendants  with 
immense  rapidity.  If  the  rate  of  multiplying  above  men- 
tioned should  continue  for  twelve  hours,  the  result  would 
be  the  production  of  about  seventeen  million  offspring. 
Such  a  rapid  production  as  this  does  not  continue  very 
long,  through  lack  of  food  and  other  adverse  conditions. 
If  it  did,  the  world  would  soon  become  filled  with  bacteria, 
crowding  everything  else  out  of  existence. 

Recognizing  that  they  have  this  wonderful  power  of 
multiplication,  we  can  readily  see  that  bacteria  represent 
a  force  in  nature  of  almost  inconceivable  magnitude. 
This  rate  of  growth  is  a  possibility  for  a  while  at  least, 
and  in  order  that  such  a  multiplication  should  continue 
it  is  only  necessary  that  the  bacteria  should  be  given 
proper  food  and  proper  conditions.  The  results  are  mar- 
velous. Although  they  are  so  small  that  a  single  one 
can  accomplish  practically  nothing  in  nature,  the  fact  that 
this  single  one  can  in  twenty-four  hours  produce  millions 
of  descendants  gives  to  bacteria  almost  unlimited  power. 
An  appreciation  of  this  fact  is  fundamental  to  an  under- 
standing of  the  action  of  bacteria.  Since  one  in  the 
course  of  a  few  hours  may  become  hundreds  of  thousands, 
and  a  little  later  its  progeny  may  be  millions,  it  is  clear 
that  in  order  to  protect  any  material  from  the  action  of 
bacteria  something  more  is  necessary  than  simply  to 
reduce  the  number  of  microorganisms.  If  the  material 
is  to  be  protected  from  them,  every  single  bacterium  must 


GROWTH    OF   BACTERIA  109 

be  destroyed,  for  if  but  one  be  left  alive  it  will  require 
only  a  few  hours  for  its  descendants  to  become  so  numer- 
ous as  to  be  able  to  accomplish  almost  anything  in  the 
way  of  chemical  destruction. 

Relation  of  Growth  to  Temperature.  This  great  power 
of  growth  is  dependent  upon  many  factors,  most  promi- 
nent among  which  is  temperature.  Like  all  living  things, 
bacteria  will  not  grow  at  the  temperature  of  freezing  or 
below,  but  will  develop 
at  nearly  all  temperatures 
above,  some  species  even 
growing  at  140.°  Certain  a*  % 
species  grow  best  at  a 
temperature  that  is  not 
much  above  freezing  ; 
others  grow  best  at 

higher  temperatures.  ^^  showing  the  effect  f  variations 
Most  of  the  common  in  temperature  on  bacteria  growth,  a, 
household  types  require  a  single  bacterium;  b,  its  progeny  in 

considerable  warmth  for       twentyfour  hours  at  5o° ;  *,  its  progeny 

in  twenty-four  hours  at  70°. 

their  proper  growth,  and 

the  warmer  the  temperature,  up  to  a  certain  limit,  the  more 
rapid  their  growth.  The  relation  of  temperature  to  the 
rapidity  of  multiplication,  for  common  species,  is  shown 
by  the  accompanying  figure  (Fig.  54).  At  a  is  repre- 
sented a  single  bacterium ;  at  b  is  the  progeny  of  this  bac- 
terium when  kept  twenty-four  hours  at  a  temperature  of 
50°,  a  little  above  that  of  the  ordinary  ice  chest  ;  at  c  is  the 
progeny  of  this  bacterium  kept  the  same  time  at  70°, 
the  ordinary  temperature  of  a  living  room.  A  glance  at 
the  figure  will  show  what  an  extraordinary  influence  a  few 


1 10  BACTERIA,  YEASTS,  AND   MOLDS 

degrees  of  temperature  may  have  upon  the  rate  of  growth 
of  this  bacterium.  The  figure  teaches  a  very  practical 
lesson  in  regard  to  the  influence  of  cold  in  delaying  the 
growth  of  bacteria  and  thus  protecting  food  from  spoiling. 

If  the  temperature  is  raised  too  high,  it  has  an  injurious 
action  upon  the  growth  of  bacteria.  Each  species  of  bac- 
teria grows  best  at  a  certain  temperature,  growing  less 
rapidly  if  warmed  above  this  point  or  cooled  below  it. 
Most,  though  not  all,  of  the  bacteria  against  which  the 
housewife  has  to  contend  grow  best  at  temperatures 
between  70°  and  95°.  If  the  temperature  is  raised  above 
95°,  many  cease  to  grow  so  rapidly,  and  at  still  higher  tem- 
peratures—  between  12 5°  and  140°-— a  large  majority  are 
quite  incapable  of  growing  at  all.  At  the  higher  temper- 
atures food  would  hardly  decay.  There  are,  however,  a 
few  species  which  grow  only  at  very  high  temperatures, 
not  developing  at  all  unless  it  is  above  125°. 

It  is  perfectly  evident  that  all  problems  connected  with 
the  protection  of  food  from  the  action  of  microorganisms 
will  be  dependent  upon  the  temperature  at  which  the  bac- 
teria grow  most  rapidly.  Food  which  is  kept  in  an  ice 
chest,  although  it  may  be  protected  from  the  action  of 
those  bacteria  which  grow  only  at  room  temperatures,  will 
be  exposed  to  other  species  that  grow  best  at  lower  tern 
peratures.  When  we  remember  that  some  kinds  of  bac- 
teria grow  at  temperatures  close  to  freezing,  we  can  readily 
see  that  no  method  of  cooling  food  short  of  actually 
freezing  it  will  totally  protect  it  from  decay. 

Death  Temperatures.  All  bacteria  are  killed  by  excess- 
ive heat,  but  the  temperature  which  kills  them  is  some- 
what variable.  Bacteria  exist,  as  we  have  seen,  in  two 


DEATH    TEMPERATURE  III 

forms.  One  is  the  active,  growing  form,  in  which  they 
feed  and  multiply  rapidly ;  the  other  is  the  spore  form,  in 
which  they  are  at  rest,  neither  feeding  nor  growing.  In 
the  former  condition  they  are  easily  killed  by  moderate 
heat,  a  temperature  of  149°  to  160°,  if  continued  for  an 
hour  (usually  a  much  shorter  time),  being  quite  sufficient 
to  destroy  them.  In  the  form  of  spores,  however,  such  a 
temperature  has  little  value  in  destroying  them.  Bacteria 
can  resist  without  being  killed  a  higher  temperature  than 
can  any  other  known  form  of  living  matter.  Spores  of 
certain  bacteria  can  be  boiled  for  a  long  time  without 
being  killed,  and  if  subsequently  cooled  they  will  grow 
and  multiply.  To  destroy  the  vitality  of  such  spores 
requires  a  temperature  above  that  of  boiling  water,  a 
temperature  rather  difficult  to  obtain,  at  least  for  liquids, 
in  an  ordinary  kitchen.  It  is,  however,  important  to 
remember  that  although  many  kinds  of  bacteria  spores 
are  not  killed  by  a  short  boiling,  a  boiling  of  an  hour  or  two 
is  sufficient  to  destroy  even  the  most  resisting  spores.  Any 
material,  therefore,  that  can  be  boiled  for  a  considerable 
length  of  time  may  thus  be  thoroughly  sterilized,  that  is, 
may  have  all  its  actively  growing  bacteria  and  all  its 
spores  destroyed  at  the  same  time.  This  great  resist- 
ance to  heat  on  the  part  of  bacteria  spores  is  a  matter 
of  much  importance  to  the  housewife,  and  she  should  fully 
realize  it.  All  canning  processes,  as  we  shall  see,  depend 
upon  the  destruction  of  bacteria,  and  the  resistance  of 
spores  to  boiling  is  a  factor  that  should  always  be 
remembered. 

A  practical  lesson  to  be  drawn  from  these  facts  is  that 
food  heated  to  boiling  in  its  preparation  is  thereby,  in  a 


112  BACTERIA,   YEASTS,  AND    MOLDS 

measure,  protected  from  spoiling,  since  the  bacteria  are 
mostly  killed.  But  if  the  food  is  simply  warmed,  the 
spoiling  is  hastened  instead  of  delayed.  For  example, 
in  making  beef  tea,  if  the  liquid  is  boiled,  it  will  keep 
easily;  but  since  boiling  precipitates  the  proteids  and 
deprives  the  material  of  most  of  its  food  value,  it  is  better 
to  make  it  by  warming  without  boiling.  Such  material 
decays  very  rapidly,  and,  if  set  on  the  back  of  the  stove  to 
keep  warm,  will  be  spoiled  in  a  short  time.  Moderate  heat 
hastens  bacteria  growth.  Boiling  kills  all  but  spores. 

Light.  Direct  sunlight  rapidly  kills  bacteria  (except 
some  spores)  and  daylight  in  general  has  an  injurious 
effect  upon  them  in  proportion  to  its  intensity.  They 
grow  best  in  darkness.  Dust  or  dirt  exposed  to  sun- 
light soon  loses  most  of  it's  living  bacteria,  while  in  dark 
cellars,  dark  corners,  and  cracks  they  may  remain  alive  a 
long  time.  Hence  the  rooms  in  our  houses  should  be 
kept  light.  The  too  frequent  habit  of  closing  blinds  and 
using  heavy  curtains  or  shutters  to  keep  out  the  light 
is  a  great  mistake.  Pantries  and  kitchens  should  have 
all  the  light  possible.  A  sick  room  particularly  should 
have  all  possible  sunlight ;  and  bright  colors  for  wall 
paper,  curtains,  etc.,  will  aid  not  only  in  making  it  cheer- 
ful but  in  actually  destroying  the  disease  bacteria.  Sun- 
light and  fresh  air  should  everywhere  take  the  place  of 
the  darkened,  closed  rooms  which  have  been  only  too 
common  in  our  houses  in  past  years. 

Relation  to  Air.  Most  living  things  require  oxygen 
and  therefore  demand  air  for  their  growth.  This  is  true 
of  a  majority  of  bacteria.  Most  bacteria  like  to  feed 
where  they  can  have  plenty  of  air.  Hence  decay  is  apt 


RELATION   TO  AIR  113 

to  begin  on  the  surface  of  things,  extending  towards  the 
interior.  This  is  not  true,  however,  of  all  bacteria.  Some 
species  can  grow  perfectly  well  without  air,  and  others, 
indeed,  cannot  grow  at  all  if  they  are  in  contact  with 
air.  The  latter  bacteria,  which  live  without  oxygen,  are 
known  as  anaerobic ;  the  former,  which  demand  oxygen, 
are  called  aerobic.  The  aerobic  bacteria  are  by  far  the  most 
important  in  the  affairs  of  the  household,  but  the  anae- 
robic bacteria,  on  the  other  hand,  produce  certain  types  of 
putrefaction  which  are  sometimes  more  serious,  inasmuch 
as  the  products  of  putrefaction  which  take  place  without 
air  are  likely  to  be  more  poisonous  than  those  products 
of  decay  taking  place  in  contact  with  the  air.  We  must 
remember,  then,  that  whereas  most  bacteria  grow  best  in 
the  air,  we  cannot  protect  any  material  from  the  growth 
of  microorganisms  simply  by  keeping  air  away  from  it, 
inasmuch  as  some  species  grow  perfectly  well,  and  even 
better,  out  of  contact  with  the  air.  Hence,  in  canning 
food,  it  is  not  the  exclusion  of  air  that  makes  preserva- 
tion of  food  possible,  but  the  exclusion  of  bacteria. 

Moisture.  Like  yeast  and  molds,  bacteria  require 
water.  Dry  food  is  protected  from  their  action  because 
they  cannot  obtain  water  sufficient  for  their  life  processes. 
Bacteria,  in  general,  require  more  water  than  molds.  Vari- 
ous materials,  if  simply  damp,  will  mold  or  mildew,  but 
they  will  not  support  bacteria  life  unless  the  amount  of 
water  is  considerable,  25  %  to  30%  of  water  being  necessary 
for  any  growth,  and  a  larger  amount  still  for  vigorous 
growth.  Hence  they  may  be  expected  to  grow  in  all 
kinds  of  food  which  are  thoroughly  wet,  but  they  will  not 
grow  in  any  of  the  dried  forms  of  food  which  we  keep 


114  BACTERIA,  YEASTS,  AND   MOLDS     . 

in  our  houses,  a  fact  of  much  importance  in  connection 
with  the  problem  of  food  preservation. 

Acidity.  For  still  another  reason  molds  and  bacteria 
do  not  commonly  flourish  upon  the  same  material.  The 
former,  as  we  have  seen,  grow  best  upon  acid  substances; 
but  most  bacteria  cannot  endure  acids,  preferring  a  slightly 
alkaline  food.  Hence  fruits,  which  are  acid,  decay  by 
molding,  while  meats,  which  are  not  so  acid  or  are  alka- 
line, decay  by  bacterial  action.  The  presence  of  acid  or 
sourness  in  food  will  check  its  decay.  Some  food  (cran- 
berries) may  be  actually  too  sour  for  bacteria  growth. 

WHERE  BACTERIA  MAY  BE  FOUND 

We  may  almost  say  they  are  to  be  found  everywhere 
upon  the  surface  of  the  earth.  This  is  not  strictly  true, 
since  a  few  places  seem  to  be  free  from  them  ;  for  exam- 
ple, the  middle  of  deserts  and  the  bottom  of  the  deep 
oceans.  But  wherever  on  the  surface  of  the  earth  ani- 
mals or  plants  are  found,  there,  in  the  earth,  the  air,  and 
all  bodies  of  water,  are  also  found  bacteria. 

Air.  Bacteria  are  so  extremely  minute  that  they  are 
capable  of  floating  in  the  air  for  a  long  time  and  of  being 
blown  by  the  winds  almost  indefinitely.  Consequently  it 
is  almost  impossible,  at  least  in  inhabited  localities,  to 
find  any  air  that  does  not  contain  them.  The  number 
that  may  be  present  in  the  air  varies  with  the  density  of 
human  population.  We  find  them  more  abundant  in  city 
than  in  country  air ;  more  abundant,  as  a  rule,  in  houses 
than  out  of  doors ;  more  abundant  in  the  air  of  rooms 
well  filled  with  people  than  in  empty  rooms,  since  they 


DISTRIBUTION    OF   BACTERIA  115 

arise  from  clothes  and  skin.  In  the  air  of  schoolrooms 
or  audience  rooms  the  number  of  bacteria  is  very  great, 
and  there  are  more  at  the  close  of  a  school  session  than 
at  the  beginning.  There  are  more  bacteria  in  the  air 
of  a  poorly  ventilated  schoolroom  than  in  the  air  of  a 
sewer.  The  presence  of  animals  as  well  as  of  men 
always  increases  the  number  of  bacteria  in  the  air. 
Wherever  we  find  dust,  there  we  find  bacteria.  By  this 
it  is  not  meant  that  dust  is  composed  wholly  of  bacteria, 
for  many  other  things  go  to 
constitute  what  we  know  as  OQ  o  •*? 
dust;  but  among  the  dust  abed 

particles  we  may  be  sure  to  _ 

x?  =»  a         <?ff  *=-,         x//- 
find    bacteria   in    great   num-    Jj|/         £^jJ      ~"5^ 

bers.      In  short,  all  air  in  the       e  ^  ' 

vicinity  of  habitation  contains 

*  FIG.  55.     A  group  of  bacteria  in 

bacteria.     The  air  of  high  water. 

mountains  far  from  the  habi- 


tat  ion   of  animals   is    found      lans'>  c>  bacillus  **t*rficiaiis  ;  <t,  ba- 

cillus  rubescens  ;  e,   bacillus  hyalinus  ; 

to  be  moderately  free  from  /,  badiius  deiicatuius  •,  g,  badiiusjan- 
these  ubiquitous  organisms. 

Elsewhere  they  are  present  in  abundance.  Since  this  is 
the  case  it  is  quite  impossible  for  any  material  exposed  to 
the  air  for  even  a  short  time  to  escape  a  rapid  contami- 
nation with  microorganisms. 

Water.  Practically  all  bodies  of  water  on  the  surface 
of  the  earth  are  filled  with  bacteria  (Fig.  55).  The 
number  found  in  water,  however,  is  widely  variable.  In 
spring  water  which  comes  fresh  from  the  ground  the 
number  is  small,  and  in  some  cases  they  may  be  wholly 
absent.  The  same  thing  is  true  of  the  water  of  artesian 


Il6  BACTERIA,  YEASTS,  AND    MOLDS 

wells,  drawn  from  a  depth  of  a  hundred  feet  or  more. 
All  surface  waters  are  sure  to  contain  them,  for  they 
are  present  in  lakes,  ponds,  pools,  rivers,  and  in  the  ocean. 
They  are  more  abundant  in  flowing  streams  than  in  water 
standing  in  lakes  or  reservoirs,  quite  contrary  to  the  usual 
belief.  We  commonly  look  upon  running  waters  as  purer 
than  standing  waters,  but,  so  far  as  concerns  bacteria,  the 
reverse  is  usually  the  case.  Rivers  or  brooks  contain  them 
in  large  numbers  ;  lakes  in  which  the  water  has  stood  for 
a  long  time  contain  a  far  smaller  quantity.  The  reason 
is  that  rivers  and  brooks  collect  the  bacteria  from  the 
surface  of  the  ground,  from  sewage,  etc.,  and  the  longer 
they  flow  the  greater  the  number  of  bacteria  they  con- 
tain, since  they  are  great  draining  agents  for  the  country. 
When  water  stands  in  lakes  or  ponds  the  bacteria,  which 
are  slightly  heavier  than  the  water,  have  a  chance  to  settle 
to  the  bottom.  This  they  do  in  the  course  of  a  few  days, 
and  after  a  time  the  water  in  such  standing  reservoirs 
becomes  far  purer  than  in  the  supply  streams.  It  will 
easily  be  understood  that  the  greater  the  amount  of 
decaying  matter  entering  any  stream  the  larger  will  be 
the  number  of  bacteria  in  its  waters.  The  rivers  of  civi- 
lized countries,  that  receive  the  sewage  from  cities,  not 
only  contain  these  little  organisms  in  immense  numbers, 
but  contain  some  of  the  most  dangerous  kinds,  since  they 
are  the  disease  germs  discharged  from  human  patients. 

From  these  general  facts  we  reach  the  conclusion  that 
no  water  at  our  command  upon  the  surface  of  the  earth  is 
absolutely  free  from  bacteria.  Spring  water  is  the  purest, 
and  water  from  deep  artesian  wells  is  about  equally  pure. 
Water  from  lakes  and  reservoirs  is  the  next  in  purity,  and 


BACTERIA   IN   THE   SOIL 


n; 


water  derived  directly  from  flowing  streams  and  rivers  is 
most  likely  to  contain  these  organisms  in  greatest  num- 
bers. The  most  dangerous  water  for  drinking  pur- 
poses is  that  of  rivers  which  have  been  contaminated  in 
any  way  by  sewage  material,  a  condition  of  things  true  of 
the  water  used  in  some  cities. 

Soil.  Soil  on  the  surface  of  the  earth  is  usually  filled 
with  bacteria  (Fig.  56).  They  are  usually  abundant  in 
the  superficial  layers,  decreasing 
rapidly  as  we  pass  below  the  sur- 
face, until  at  the  depth  of  a  com- 
paratively few  feet  they  practi- 
cally disappear.  They  are  more 
abundant  in  some  kinds  of  soil 
than  in  others.  Where  the  soil 
is  dry  and  sandy  the  number  is 
comparatively  small;  where  it  is 
moist  and  loamy  they  are  more 
abundant.  They  are  found  pro- 
fusely around  buried  bodies  of 
animals,  or  in  soil  that  contains 
decaying  roots  of  ordinary  plants. 
They  are  immensely  numerous 
in  the  vicinity  of  earth  closets 
or  privies,  and  the  soil  near  sink  drains  and  manure  heaps 
is  filled  with  them.  Indeed,  any  soil  which  contains  the 
remains  of  animal  or  vegetable  matter  and  a  considerable 
amount  of  moisture  will  have  bacteria  in  inconceivable  num- 
bers, while  in  cleaner  soils  they  will  be  much  less  abundant. 

They  are  sure  to  be  abundant  in  all  dirt  which  accu- 
mulates in  a  household,  for  nearly  all  such  dirt  contains 


FIG.  56.     A  group  of  soil 
bacteria. 


fusiformi*-,  e,  B.subtms-,  /, 

terium  pasteuriana. 


n8 


BACTERIA,  YEASTS,  AND  MOLDS 


organic  material  in  a  state  of  partial  decay.  Any  dirt 
which  collects  in  corners  of  rooms,  in  the  cracks  of  floors, 
or  upon  shelves  in  pantries,  cellars,  etc.,  is  sure  to  contain 
bacteria  in  great  quantities.  The  dirt  that  clings  to  the 
walls  and  ceilings  of  rooms  is  also  quite  sure  to  contain 


FIG.  57.     A  bit  of  decaying  meat  highly  magnified,  show- 
ing the  bacteria  feeding  upon  the  material. 

them,  and  the  dirt  collected  by  sweeping  the  floors  is  filled 
with  them. 

Bacteria  in  Food.  Bacteria  are  found  in  all  moist  foods, 
especially  in  those  undergoing  the  process  commonly 
spoken  of  as  spoiling  (Fig.  57).  Indeed  it  is  the  bac- 
teria, as  we  shall  presently  see,  that  ordinarily  cause 
this  spoiling.  Any  meat  which  develops  the  gamy  flavor 


BACTERIA   IN   FOOD  119 

is  filled  with  them ;  sour  milk  contains  them  in  immense 
numbers  ;  moldy  bread  and  bad  eggs  hold  millions  of  them, 
and  decaying  fruit  may  show  bacteria  as  well  as  molds. 
All  types  of  food  which  develop  peculiar  taints  and  tastes 
characteristic  of  putrefaction  contain  great  numbers  of 
bacteria.  Long  before  these  taints  are  appreciable  to 
the  senses  the  bacteria  that  produce  them  are  abundant. 
No  moist  food  can  be  exposed  on  pantry  shelves  or  in 
ice  chests,  even  for  an  hour,  without  containing  bacteria, 
and  after  it  has  remained  there  for 
a  day  or  two  the  number  of  bac- 
teria present  in  it  becomes  very 
great  indeed,  because  of  the  multi- 
plication of  those  that  have  found 
entrance. 

In  the  Body.  The  presence  of 
bacteria  in  food  leads  us  to  expect  FIG-  58-  Bacteria  from  the 
to  find  them  in  our  mouths,  stom-  teeth  of  a  health?  mouth' 
achs,  and  intestines.  Our  whole  digestive  tract  is  crowded 
with  them.  Fig.  58  represents  a  bit  of  the  scrapings  from 
the  teeth,  highly  magnified,  and  containing  hundreds  of 
several  different  species  of  bacteria.  They  are  equally  or 
more  abundant  in  the  stomach  and  intestines.  This  is 
the  normal  condition  of  things,  and  these  bacteria  do  us 
no  injury,  but  are  probably  of  direct  use. 

The  substance  of  the  matter  is  that  bacteria  are  practi- 
cally everywhere  on  the  surface  of  the  earth.  They  are 
in  immense  numbers  in  the  household,  on  the  walls  and 
ceilings  of  our  rooms,  upon  our  pantry  shelves ;  they 
are  present  in  every  bit  of  food  which  remains  exposed 
to  the  air  for  a  short  time ;  they  are  in  all  liquid  foods, 


120  BACTERIA,   YEASTS,  AND    MOLDS 

particularly  milk.  So  ubiquitous  are  they  that  it  is  an 
absolute  impossibility  for  the  housewife,  by  any  means 
at  her  command,  to  keep  her  pantry  and  food  free  from 
them. 

These  facts  forcibly  emphasize  the  futility  of  the  com- 
mon method  of  sweeping  and  dusting  rooms.  Bacteria 
are  heavier  than  the  air  and  if  undisturbed  settle  and  lie 
quietly  upon  floors,  tables,  etc.  Every  sweeping  the  room 
receives  stirs  them  up.  A  dustbrush  sends  them  flying 


FIG.  59.     Petri  dishes  exposed,  one,  a,  before,  and  the  other,  3, 
after  a  class  has  occupied  a  schoolroom. 

through  the  room  only  to  settle  down  again  later.  On  the 
other  hand,  wiping  with  damp  cloths  removes  the  bacteria 
and  is  the  only  proper  method  of  cleaning.  This  is  espe- 
cially true  for  kitchens  and  pantries  where  food  is  exposed 
to  the  air,  and  for  schoolrooms  where  there  is  likely  to  be 
a  collection  of  numerous  kinds  of  bacteria,  including  some 
disease  germs  brought  by  the  many  children.  Fig.  59 
shows  two  plates,  one  exposed  to  the  air  before  and  the 
other  after  a  school  session.  The  relative  abundance  of 
bacteria  floating  in  the  air  is  clearly  shown. 


RESULTS   OF   BACTERIA   GROWTH  121 

These  facts,  too,  show  the  desirability  of  having  the 
walls  of  kitchens  and  pantries  smooth  and  glazed,  in  order 
that  they  may  not  furnish  lodging  places  for  air  bacteria 
and  may  be  cleaned  readily  with  a  damp  cloth.  They  also 
show  us  that  lace  curtains  and  heavy  hangings  around 
rooms  will  be  lurking  places  for  numerous  organisms. 
This  may  do  no  harm  in  ordinary  parlors,  rooms  where 
the  bacteria  are  mostly  harmless  and  where  no  food  is 
kept,  but  should  never  be  allowed  in  kitchens,  and  should 
be  most  emphatically  forbidden  in  sick  rooms  where  dis- 
ease germs  are  likely  to  be  floating  about  in  the  air. 

THE  RESULTS  OF  BACTERIA  GROWTH 

The  bacteria  with  which  we  are  concerned  all  require 
complex  foods.  Some  species  can  live  upon  simple  min- 
erals from  the  soil,  but  these  are  of  no  importance  in  the 
household.  All  that  are  of  interest  for  our  purposes  feed 
upon  substances  quite  similar,  in  general,  to  those  upon 
which  animals  subsist.  Any  materials  containing  sugars, 
starches,  proteids  (albumen,  lean  meat,  etc.),  or  other  ani- 
mal foods,  furnish  excellent  nourishment  for  bacteria. 
For  this  reason  the  bacteria  are  in  a  sense  the  rivals  of 
the  animal  kingdom.  Both  animals  and  bacteria  feed  upon 
the  same  kind  of  food,  and  both  are,  therefore,  constantly 
seeking  to  obtain  and  use  it  for  their  own  purposes. 

When  we  bear  in  mind  the  facts  thus  far  outlined  we 
can  easily  understand  why  bacteria  play  such  an  important 
part  in  the  affairs  of  everyday  life.  They  are  too  small  to 
see,  but  are  capable  of  inconceivably  rapid  multiplication. 
They  are  all  about  us  in  great  numbers,  in  earth,  air,  and 


122  BACTERIA,   YEASTS,  AND   MOLDS 

water.  Some  can  be  dried  without  injury,  others  frozen 
for  months  without  losing  their  vitality,  and  even  a  short 
boiling  fails  to  kill  many  species.  With  all  these  wonder- 
ful properties  it  is  not  strange  that  they  are  constantly  at 
work  all  around  us  modifying  the  nature  of  all  substances 
upon  which  they  feed. 

PARASITES  AND  SAPROPHYTES 

The  food  upon  which  bacteria  feed  may  be  either  living 
or  dead.  If  bacteria  are  capable  of  feeding  upon  the 
living  body  of  an  animal  or  plant,  we  call  them  parasites. 
Such  bacteria  quite  naturally  produce  injury  to  the  life 
of  the  individual  upon  which  they  feed.  In  mankind  they 
produce  a  great  variety  of  abnormal  results  which  we  call 
diseases.  The  parasitic  bacteria,  therefore,  are  commonly 
called  disease  germs,  and  are  the  cause  of  most  of  our  con- 
tagious diseases.  Many 'of  them  feed  upon  animals,  pro- 
ducing animal  diseases,  while  others  live  upon  plants, 
giving  rise  to  diseases  in  the  plant  world. 

Fortunately  only  a  comparatively  small  number  of  spe- 
cies of  bacteria  are  capable  of  existing  upon  living  bodies 
of  animals.  The  great  majority  are  incapable  of  feeding 
upon  living  tissue,  although  they  feed  upon  it  readily 
enough  after  it  is  dead.  Those  dependent  upon  the  dead 
bodies  of  animals  or  plants  cannot  live  a  parasitic  life. 
When  bacteria  feed  upon  such  nonliving  materials  we  call 
them  saprophytes.  They  are,  like  animals  in  general,  depend- 
ent for  sustenance  upon  dead  animal  and  vegetable  food 
The  saprophytic  bacteria,  while  they  may  be  rivals  of  ani- 
mals for  food,  are  not  the  cause  of  diseases.  These  harmless 


SAPROPHYTES   AND    PARASITES  123 

bacteria  far  outnumber  the  disease  germs.  We  should 
not  therefore  be  frightened  when  we  learn  that  bacteria 
are  all  around  us,  in  the  food  we  eat,  the  water  we  drink, 
and  the  air  we  breathe.  Most  of  them  are  harmless  or 
beneficial,  and  need  cause  us  no  uneasiness. 

It  should  also  be  noted,  finally,  that  some  bacteria  can 
live  both  upon  living  tissues,  like  parasites,  and  upon 
dead  material,  like  saprophytes.  Such  microorganisms 
are  partly  parasitic  and  hence  are  capable  of  producing 
disease.  They  are  also  capable  of  living  outside  the  body 
in  various  localities  in  nature.  They  may  be  of  serious 
importance  to  the  health  of  man,  inasmuch  as  they  are 
capable  of  living  a  parasitic  life  if  they  can  get  into  the 
living  body ;  but  are  also  able  to  live  an  independent  life 
in  nature.  All  disease  bacteria  either  belong  to  this  class 
or  are  strict  parasites,  while  the  harmless  bacteria  belong 
to  the  class  of  saprophytes. 


CHAPTER    IX 

BACTERIA  WHICH   LIVE   UPON   DEAD  FOOD: 
SAPROPHYTES 

These  include  the  bacteria  found  living  freely  in  nature, 
in  the  air,  in  water,  and  in  the  soil.  Since  they  live  upon 
dead  organic  material  they  may  be  expected  in  any  kind 
of  food  upon  which  the  human  being  lives,  as  well  as  in 
other  substances  that  do  not  serve  us  as  food. 

MATERIALS  THAT  SERVE  BACTERIA  AS  FOOD 

Some  kinds  of  food  are  very  readily  attacked  by  bac- 
teria, others  with  more  difficulty,  and  some  hardly  at  all. 
Pure  sugars  are,  as  a  rule,  not  attacked  by  them,  although 
if  the  sugar  is  in  water  solution  certain  bacteria  may  some- 
times feed  upon  it,  and  raw  sugar  is  sometimes  injured 
by  bacterial  growth.  The  same  is  true  of  pure  starches, 
since  most  bacteria  are  quite  incapable  of  making  use  of 
pure  starch.  It  happens,  however,  that  nearly  all  of  our 
food  materials  containing  starch  and  sugar  contain  also 
other  substances  upon  which  bacteria  can  feed,  so  that 
the  sugary  and  starchy  foods  in  our  households  are  by  no 
means  exempt  from  them.  Fats  are  also  attacked  by  bac- 
teria, although  less  readily  than  some  foods.  By  bacterial 
action  the  fat  is  made  rancid  and  undergoes  other  less 
familiar  changes. 

124 


FOODS    OF   BACTERIA  12$ 

The  food  most  readily  attacked  by  the  majority  of  bac- 
teria is  the  class  known  as  proteids.  Proteid  materials 
are  foods  for  nearly  all  species  of  bacteria,  are  most  easily 
attacked  by  them,  and  are  sure  to  be  consumed  if  exposed 
to  the  air  under  proper  conditions.  By  proteid  food  is 
meant  a  class  of  chemical  substances,  highly  complex  in 
nature,  which  may  best  be  understood  by  illustrations. 
The  best  known  examples  are  the  following :  the  white 
of  egg,  named  albumen;  the  lean  part  of  meat,  known 
by  chemists  as  myosin ;  the  curd  of  milk,  called  casein; 
gluten,  which  is  the  gummy  substance  present  in  wheat 
flour  ;  a  similar  substance  present  in  beans,  known  as 
legumen.  All  of  these  substances  will  be  recognized  as 
liable  to  putrefy  rapidly.  Nearly  all  of  our  foods  contain 
either  these  proteids  or  others  in  greater  or  less  abun- 
dance. Anything  made  of  flour  contains  gluten  ;  any- 
thing that  has  milk  in  it  contains  casein  ;  all  meats 
contain  myosin  ;  anything  made  of  beans  or  peas  contains 
the  legumen,  while  eggs  always  furnish  albumen.  Since 
most  foods  contain  some  of  these  substances,  and  since 
cooking  does  not  change  their  nature,  practically  all  foods 
hold  some  of  these  proteids. 

Proteids  are  of  all  foods  the  most  necessary  for  the 
human  body.  While  the  body  might  live  on  proteids 
alone,  it  could  not  live  entirely  on  any  other  kind  of  food, 
and  proteids  therefore  are  absolutely  necessary  for  the 
human  body.  Most  bacteria  flourish  upon  proteids  as  well 
as  we  do,  and  inasmuch  as  practically  all  of  our  food 
products  contain  a  certain  quantity  of  proteids,  it  follows 
that  nearly  all  of  our  foods  are  readily  consumed  by  the 
great  host  of  saprophytic  bacteria. 


126  BACTERIA,   YEASTS,  AND    MOLDS 

THE  EFFECT  OF  BACTERIAL  GROWTH  UPON  FOOD 

If  any  common  food  product  is  sufficiently  moist,  bac- 
teria which  get  into  it  from  some  source  are  sure  to  grow 
and  in  the  course  of  a  few  hours  will  produce  marked 
changes  therein.  But  bacteria  do  not  consume  food  as 
large  animals  do  by  taking  it  bodily  inside  of  themselves. 
They  are  quite  too  small  to  do  this.  To  the  eye  it  does  not 
seem  that  the  bacteria  are  actually  consuming  the  food 
but  that  they  are  simply  producing  noticeable  changes 
within  it.  In  reality,  however,  they  are  consuming  it 
and  in  the  end  cause  its  almost  complete  disappearance. 
The  essential  effect  that  they  produce  is  the  chemical 
decomposition  of  the  material  upon  which  they  are  feed- 
ing. Bacteria  do  not  consume  the  whole  food  but  use 
only  a  part  of  it.  An  illustration  may  make  clear  their 
mode  of  action.  If  a  house  is  built  with  a  wooden 
frame  and  brick  walls,  and  the  wood  is  burned  away,  the 
house  is  sure  to  tumble  to  pieces,  because  the  wooden 
framework  is  necessary  to  hold  the  building  together. 
Much  the  same  thing  is  true  of  a  chemical  molecule,  which 
is  a  structure  made  of  a  variety  of  substances  bound 
together  to  form  a  unit.  Bacteria,  as  they  utilize  foods, 
have  the  power  of  taking  some  of  these  materials  out  of 
the  molecule,  but  cannot  consume  the  whole.  The  result 
of  extracting  some  of  the  material  from  a  molecule  is  that 
the  entire  structure  will  fall  to  pieces,  just  as  the  house 
falls  whose  framework  has  been  burned  away.  The  meat 
becomes  putrid,  the  milk  sours,  the  egg  rots,  and  any 
other  material  containing  proteid  undergoes  a  similar  type 
of  spoiling. 


PRODUCTS   OF  BACTERIAL   GROWTH  I2/ 

NEW  PRODUCTS 

Decomposition  Products.  When  a  house  falls  to  pieces 
after  burning,  a  mass  of  debris  is  left  lying  in  the  old  cellar. 
So,  when  the  chemical  molecule  is  broken  to  pieces,  as 
described  above,  there  will  remain  certain  fragments  of 
the  original  molecule.  Although  really  fragments  of  the 
original  substances  they  are  quite  different  in  nature  from 
the  original  material.  They  are  known  as  by-products  of 
decomposition,  or  simply  as  decomposition  products.  When- 
ever bacteria  grow  in  a  mass  of  food,  destroying  the 
chemical  nature  of  the  food  molecules,  there  is  sure  to  be 
produced  a  variety  of  materials  representing  the  de"bris 
from  the  destruction  of  the  molecule.  These  materials 
are  by-products  of  decomposition  and  are  always  of  a 
nature  quite  different  from  the  original  food  substance. 
They  are,  as  a  rule,  simpler  in  their  chemical  nature  than 
the  original  food,  and  are  quite  different  in  their  physical 
characters. 

From  the  original  food,  which  may  have  been  a  partly 
solid  material,  like  a  bit  of  meat,  there  arises  as  the  result 
of  its  destruction  a  number  of  these  by-products,  some  of 
which  are  in  the  form  of  gases  and  pass  off  into  the  air, 
some  of  which  are  more  or  less  liquid  and  remain  behind 
in  the  food  mass.  Others  are  easily  soluble  in  water  and 
dissolve  in  the  liquids  of  the  food.  Thus  the  food  material 
is  almost  sure  to  soften  gradually  and  to  become  of  a  more 
or  less  fluid  nature.  There  is  likely  to  be  a  considerable 
variety  of  these  by-products,  some  of  them  having  new 
odors  and  tastes.  The  new  materials  give  to  the  food 
mass  as  it  is  consumed  by  bacteria  wholly  new  flavors ; 


128  BACTERIA,   YEASTS,  AND    MOLDS 

and  since  some  of  them  are  vapors  they  may  give  it  a 
strong  odor.  Consequently  the  food  material  which  is 
being  consumed  by  bacteria  soon  begins  to  have  a  very 
strong  taste  and  odor,  due  to  some  of  these  decomposition 
products.  The  character  of  the  food  changes  very  greatly, 
and  after  the  bacteria  have  had  an  opportunity  of  feeding 
upon  the  material  for  a  comparatively  few  hours  no  resem- 
blance to  the  original  food  mass  remains,  in  appearance, 
taste,  or  smell. 

This  whole  phenomenon  is  spoken  of  as  putrefaction,  or 
decay.  There  is,  however,  a  slight  difference  between 
these  two  terms.  By  putrefaction  we  commonly  mean  a 
change  in  food  masses  by  which  a  series  of  very  unpleas- 
ant odors  and  tastes  make  their  appearance  in  the  putre- 
fying mass.  By  the  term  "decay"  we  properly  mean  a 
more  complete  destruction  of  the  food  material,  in  which 
the  unpleasant  odors  and  flavors  finally  disappear,  leaving 
behind  a  comparatively  odorless  material  which  represents 
the  final  debris  remaining  from  the  total  destruction  of 
the  food  masses.  Putrefaction,  with  its  high  flavors  and 
odors,  is  an  incomplete  process ;  decay,  a  more  complete 
process  of  destruction.  Putrefaction  is  produced  in  gen- 
eral by  bacteria  when  they  do  not  have  an  abundance  of 
air  or  oxygen,  whereas  decay  occurs  when  the  amount  of 
air  or  oxygen  present  is  abundant.  In  other  words,  when 
a  bit  of  food  is  being  consumed  by  bacteria  without  suffi- 
cient oxygen  it  putrefies  and  becomes  offensive  in  taste 
and  smell ;  when,  however,  the  oxygen  is  abundant,  the  pro- 
cess of  putrefaction  goes  on  to  a  more  complete  destruc- 
tion, ending  finally  in  what  is  known  as  decay,  by  which 
the  material  is  converted  into  inoffensive  substances. 


BACTERIAL   SECRETIONS  129 

Bacterial  Secretions.  Besides  the  decomposition  prod- 
ucts just  referred  to,  another  class  of  new  substances  is 
found  in  the  putrefying  and  decaying  food,  and  these  are 
to  be  regarded  as  secretions  from  the  bacteria.  Bacteria  are 
living  organisms  and,  like  larger  animals  and  plants,  are  con- 
stantly emitting  from  their  bodies  certain  secretions.  Our 
own  bodies  are  constantly  secreting  materials,  like  perspira- 
tion, urea,  etc. ;  and  bacteria,  as  the  result  of  their  activity, 
are  also  constantly  producing  a  small  amount  of  secretions. 
These  secretions  are  totally  different  products  from  the 
original  food.  The  secretions  from  some  species  of  bac- 
teria are  quite  harmless,  although  others  are  of  an  intensely 
poisonous  nature.  As  a  result,  a  bit  of  food  that  is  under- 
going putrefaction  may  in  the  course  of  time  become 
highly  poisonous  because  of  the  appearance  of  poisonous 
materials,  part  of  which  may  be  decomposition  products 
but  most  of  which  are  probably  bacterial  secretions. 

Chemists  and  bacteriologists  are  not  able  to  separate 
very  clearly  decomposition  products  from  the  secretions 
of  bacteria,  and  for  our  purpose  it  is  quite  unnecessary. 
We  need  only  remember  that  as  the  bacteria  consume  our 
food  products  they  produce  profound  chemical  changes 
which  we  call  putrefaction  and  decay.  As  the  result  of 
these  changes  not  only  is  a  host  of  highly  flavored  prod- 
ucts developed  but  also  another  series  with  strong  odors. 
Some  of  these  new  products  are  poisonous,  others  are  not. 
All  of  them  have  a  tendency  to  be  softer  than  the  original 
food  and  more  easily  dissolved  in  water;  the  result  of  which 
is  that  as  the  food  is  consumed  by  the  bacteria  it  becomes 
softer  and  more  liquid.  In  the  end  it  largely  disappears, 
being  dissolved  into  gases  which  pass  off  into  the  air  and 


130  BACTERIA,  YEASTS,  AND   MOLDS 

liquids  that  soak  down  into  the  soil  or  evaporate,  leaving 
only  a  small  residue.  This  is  the  general  phenomenon  of 
putrefaction,  ending  in  complete  decay. 

Advantages  from  Incipient  Decay.  Although  this  pro- 
cess of  decay  may  be  a  somewhat  rapid  one,  it  actually 
takes  place  by  steps,  one  after  another.  The  breaking 
down  of  the  food  under  the  action  of  bacteria  is  not  a 
sudden  falling  of  the  molecules  into  fragments  but  a  pro- 
cess that  takes  considerable  time  and  presents  a  number 
of  intermediate  steps  between  the  original  food  and  the 
final  condition  of  decay.  As  the  bacteria  begin  to  act 
upon  the  food  it  is  not  at  first  necessarily  ruined  or  even 
injured.  At  the  beginning  of  the  process  the  new  prod- 
ucts are  quite  different  from  those  that  appear  later,  and 
it  may  happen  that  those  first  produced  give  to  the  food 
a  slight  flavor  which,  instead  of  injuring  its  character, 
actually  improves  it. 

The  presence  of  a  certain  amount  of  flavor  in  our  foods 
is  very  desirable,  and  even  necessary.  Pure  foods  with- 
out flavors  cannot  be  properly  digested  and  absorbed,  a 
certain  amount  of  flavor  being  needed  to  stimulate  the 
digestive  organs.  Some  of  the  flavors  arising  in  the  early 
stage  of  decomposition  are  of  a  character  that  is  enjoyed 
by  the  human  palate.  For  example,  the  so-called  gamy 
taste  of  meat  is  a  flavor  which  some  people  enjoy  very 
much,  while  others  dislike  it.  This  gamy  taste  is  simply 
the  beginning  of  decomposition,  and  is  due  to  the  fact 
that  the  meats  have  been  kept  until  the  bacteria  have 
begun  to  act  upon  them  and  to  produce  the  incipient 
stages  of  putrefaction.  In  this  early  period  the  flavors 
are  not  very  strong  and  not  particularly  unpleasant ;  but 


FLAVORS   FROM    INCIPIENT   DECAY  131 

if  the  process  is  allowed  to  go  a  little  farther  the  taste  of 
putrefaction  becomes  too  strong  for  any  palate.  Another 
example  is  Limburger  cheese,  in  which  a  strong  flavor 
of  incipient  putrefaction  is  produced  by  the  development 
of  bacteria  in  the  cheese  mass.  Any  one  who  has  ever 
known  the  flavor  or  taste  of  Limburger  cheese  will  easily 
believe  that  it  is  incipient  putrefaction.  Other  forms  of 
soft  cheeses  show  the  same  feature  in  less  degree.  A 
great  variety  of  flavors  and  odors  is  found  in  the  so-called 
soft  cheeses,  nearly  every  one  of  which 
represents  a  certain  type  of  incipient  pu- 
trefaction. Even  the  hard  cheeses  show 
this  same  characteristic,  though  there  is 
less  similarity  to  putrefaction.  Neverthe- 
less the  taste  of  the  hard  cheese  is  prob-  FlG-  6o-  Bacterium 
ably,  at  least  in  part,  due  to  the  beginning  ^r°  mgKg*?C 

'  flavors  in  butter. 

of  this  process  of  chemical  destruction 
produced  by  bacteria.  If  the  cheese  has  become  over- 
ripened,  a  very  strong  decayed  taste  may  be  apparent. 
In  the  making  of  butter  the  same  phenomenon  occurs,  for 
the  extremely  delicate  flavor  of  a  high  quality  of  butter 
is  due  to  the  action  of  bacteria  upon  the  cream  before 
the  butter  is  made,  and  the  butter  flavor  is  thus  one  of 
incipient  decay  (Fig.  60).  It  is  one  of  the  most  exquisitely 
delicate  of  all  our  food  flavors,  and  is  highly  enjoyed  by 
all  people. 

VINEGAR 

Another  example  of  a  benefit  derived  from  bacterial 
action  is  in  the  manufacture  of  vinegar.  This  is  a  mate- 
rial which,  though  not  a  real  food,  is  used  in  considerable 


132  BACTERIA,   YEASTS,  AND   MOLDS 

quantities  as  a  condiment  and  preservative.  As  ordinarily 
made  it  is  simply  a  product  of  bacterial  growth.  The 
basis  of  vinegar  is  acetic  acid,  and  this  is  produced  from 
alcohol  by  certain  changes  brought  about  in  it  through 
the  action  of  microorganisms.  The  source  of  vinegar  is 
always  some  weak  alcoholic  solution,  commonly  cider  or 
weak  wine;  but  any  liquid  that  contains  a  moderate 
quantity  of  alcohol  may  be  a  source  of  vinegar.  This 
material  is  caused  to  undergo  a  chemical  change  which 
converts  the  alcohol  into  acetic  acid,  and  when  this  occurs 
it  becomes  vinegar. 

*  The  change  of  the  alcohol  into  acetic  acid  is  brought 
about  by  the  presence  of  a  material,  a  brownish,  felted, 
slimy  mass,  which  increases  in  amount  as  the  vinegar  is 
made,  and  upon  whose  presence  the  conversion  of  alcohol 
into  vinegar  seems  to  depend.  This  has  long  been  known 
as  mother  of  vinegar.  „  Good  vinegar  will  always  contain  such 
mother.  The  study  of  this  mother  of  vinegar  shows  it 
to  be  a  mass  of  bacteria  (Fig.  61).  They  are  crowded 
together  in  countless  millions  to  form  this  slimy  mass, 
and  during  the  production  of  the  vinegar  multiply  rapidly 
and  finally  become  excessively  numerous.  The  growth  of 
the  bacteria  produces  the  change  in  the  alcohol  which  con- 
verts it  into  acetic  acid.  The  formation  of  common  vinegar 
is  therefore  due  to  the  development  of  microorganisms. 
Some  types  of  a  cheap  product  are  made  by  a  chemical 
process,  but  all  good  table  vinegar  is  produced  by  bacteria. 
A  knowledge  of  the  manufacture  of  vinegar  is  to-day  a 
matter  of  little  importance  in  the  household,  for  the  mate- 
rial is  commonly  made  either  in  large  factories  or  in  a 
farmer's  cellar.  The  housewife  is  simply  concerned  in 


VINEGAR 


133 


purchasing  a  good  product,  and  in  its  use.  The  type  of 
vinegar  commonly  regarded  as  the  best  is  that  which  is 
made  from  cider,  although  a  large  part  of  the  vinegar  used 
in  the  world  is  made  from  some  other  source  of  alcohol 
(wine,  beer,  etc.).  Thevalue 
of  vinegar  is  in  a  measure 
dependent  upon  its  flavor, 
which  differs  according  to 
the  material  from  which 
it  is  made.  Vinegar,  of 
course,  has  always  an  in- 
tensely sour  taste  from  the 
presence  of  acetic  acid,  but 
in  addition  to  this  there 
are  other  flavors,  due  to 
the  original  material  from 
which  it  is  produced,  and 
these  affect  its  value. 
Vinegar  also  varies  in  color 
according  to  the  substance 
from  which  it  is  made. 
Cider  vinegar  is  of  a  rich 
brown  color,  while  if  made 
from  other  materials  it 
may  have  a  reddish  or  whitish  color,  or  may  be  almost 
black.  The  color,  therefore,  is  no  indication  of  the  char- 
acter of  the  vinegar,  for  a  perfectly  good  product  may  be 
white,  red,  or  brown.  The  market  value  of  vinegar  is 
dependent  chiefly  upon  the  amount  of  acid  it  contains. 
The  higher  the  percentage  of  acid  (the  sourer  it  is),  other 
things  being  equal,  the  greater  its  value. 


FIG.  61.    Bacteria  producing  vinegar. 


134  BACTERIA,  YEASTS,  AND   MOLDS 

Although  they  are  not  bacteria  a  word  may  be  said  in 
regard  to  the  vinegar  eels  frequently  found  in  good  cider 
vinegar.  These  are  minute  little  worms,  just  visible  to  the 
naked  eye,  which  are  frequently  seen  swimming  near  the 
surface.  Their  presence  may  be  consistent  with  a  good 
quality  of  vinegar.  They  do  not  themselves  have  much 
influence  upon  vinegar,  although  if  abundant  they  weaken 
its  strength.  They  are  quite  harmless  to  the  person  using 
the  vinegar,  and  one  need  never  be  suspicious  or  throw 
away  any  because  it  contains  large  numbers  of  these  eels. 
They  must  be  looked  upon  as  present  in  ordinary  good 
cider  vinegar,  and  must  be  classed  among  the  perfectly 
harmless  organisms  which  are  sure  to  occur  in  some  of 
our  food  products. 

FOOD    EVENTUALLY    RUINED    BY    BACTERIA 

These  illustrations  are  sufficient  to  show  that  the  by- 
products of  decomposition  are  not  always  necessarily  dis- 
advantageous to  our  foods.  If  the  chemical  destruction 
is  only  beginning,  the  result  may  be  of  a  pleasant  nature, 
and  the  food  may  be  actually  benefited  by  the  action  of 
the  bacteria.  If,  however,  this  process  is  allowed  to  go 
farther,  most  foods  are  entirely  ruined.  Gamy  food  soon 
becomes  putrescent ;  soft  cheeses  of  all  kinds  soon  undergo 
putrefaction  and  decay,  and  even  the  hard  cheese  in  the 
end  will  become  ruined  by  the  development  of  too  strong 
a  flavor  of  putrefaction.  Butter  in  the  course  of  time  is 
also  ruined,  although  bacteria  do  not  grow  readily  in  butter 
and  it  may  be  kept  a  long  time  without  undergoing  putre- 
faction. It  is,  however,  really  impossible  to  draw  any 


GARBAGE  135 

due  between  the  incipient  decomposition  that  benefits 
the  flavor  of  food  and  the  later  stages  which  utterly 
destroy  it. 

Although  the  flavors  of  incipient  decomposition  may  be 
pleasant  and  useful,  the  taste  produced  by  later  stages  is 
offensive.  In  the  end  the  food  is  always  totally  ruined, 
for  bacteria  will  finally  produce  the  complete  destruction 
of  the  materials  upon  which  they  feed.  The  kinds  of 
putrefaction,  that  is,  the  odors  and  tastes  that  develop,  are 
by  no  means  always  the  same.  Different  species  of  bac- 
teria produce  different  results,  and  the  same  species  of 
bacteria  produces  a  quite  different  kind  of  decay  in  differ- 
ent sorts  of  food  material.  But  it  is  a  matter  of  little 
significance  what  type  of  putrefaction  occurs,  for  all  of 
them  are  equally  sure  to  destroy  the  food.  It  is  useful  to 
remember,  however,  that  the  kind  of  decomposition  which 
is  produced  when  bacteria  grow  without  sufficient  air  is 
always  more  unpleasant  and  more  dangerous  than  that 
which  takes  place  where  there  is  plenty  of  air.  Any  food 
material  which  is  closed  in  tight  bottles  or  jars  and  under- 
goes putrefaction  is  sure  to  give  rise  to  more  unpleasant 
odors  and  tastes  and  to  decidedly  more  unpleasant  types 
of  decomposition  than  food  material  which  decays  in  the 
open  air. 

GARBAGE 

All  the  refuse  from  our  tables  or  our  kitchens  is  just 
as  good  food  for  bacteria  as  is  the  material  which  we 
actually  consume,  and  all  of  this  waste  material,  after  we 
have  discarded  it,  is  attacked  by  bacteria.  This  is  shown 
simply  enough  by  the  odors  arising  from  garbage  if  it  is 


136  BACTERIA,   YEASTS,  AND   MOLDS 

allowed  to  stand,  the  putrefaction  and  decay  that  set  in 
being  sure  indications  of  the  presence  of  bacteria  and 
proofs  that  the  bacteria  are  decomposing  the  material. 
Such  waste  material  is,  of  course,  of  no  use  in  the  house- 
hold, since  it  is  not  in  a  condition  to  attract  the  palate  of 
man ;  but  there  is  a  large  amount  of  food  material  left 
in  these  waste  products  which  is  very  useful  for  feeding 
certain  animals.  It  has  commonly  been  used  for  feeding 
hens  and  hogs,  and  the  recognition  of  its  food  value  has 
in  recent  years  made  the  garbage  of  our  large  cities  a 
very  valuable  product.  This  use  of  garbage  is  being 
abandoned  as  unhealthful,  and  the  practice  of  burning  the 
material  is  becoming  common. 

The  housewife  is  not,  however,  concerned  in  this  prob- 
lem but  only  in  the  proper  disposal  of  the  waste  material 
from  her  kitchen  and  her  table.  This  she  simply  desires 
to  get  rid  of,  and  its  tendency  to  rapid  putrefaction  makes 
it  imperative  that  it  be  disposed  of  at  once  and  not  allowed 
to  accumulate.  She  can  adopt  a  variety  of  methods  for 
this  purpose.  She  may  burn  it,  provided  it  is  not  too  large 
in  quantity,  is  not  too  moist,  and  she  has  a  fire  hot  enough 
for  the  purpose.  As  a  rule,  however,  burning  garbage 
in  an  ordinary  kitchen  stove  is  not  very  feasible.  It  is 
commonly  too  moist  to  be  easily  consumed  in  a  moderate 
fire ;  but  where  possible  this  is  the  best  means  of  getting 
rid  of  the  waste. 

The  usual  method  of  disposing  of  garbage  in  a  city  is 
to  allow  it  to  be  removed  by  those  who  pay  for  the  privi- 
lege because  of  the  value  of  the  material  for  feeding  hogs. 
The  household  waste  is  placed  in  receptacles,  which  are 
emptied  by  the  garbage  collectors.  In  order  that  such 


GARBAGE  137 

receptacles  may  be  kept  in  a  tolerably  wholesome  con- 
dition, the  garbage  should  be  removed  frequently,  and 
for  this  we  must  depend  upon  the  faithfulness  of  the  col- 
lectors. The  vessels  themselves  should  occasionally  be 
cleaned.  If  not  cleaned,  they  give  rise  to  unpleasant, 
unwholesome  odors  in  or  around  the  house.  They  may 
become  the  breeding  places  for  flies  and  prove  to  be  in 
general  a  considerable  nuisance. 

The  chief  trouble  with  such  garbage  cans  is  their  smell 
and  unsightliness,  but  these  difficulties  are  removed  if  the 
cans  are  kept  clean.  It  is  not  difficult  to  clean  them.  Cold 
water  for  washing  garbage  cans  is  of  very  little  use  ;  but  if 
they  are  thoroughly  washed  with  very  hot  water  they  can  be 
kept  so  clean  that  they  emit  no  odor  and  are  not  unpleas- 
ant. Since  putrefaction  is  due  to  bacterial  growth  it  is  of 
course  possible  to  prevent  the  smell  and  decay  of  the  gar- 
bage by  the  use  of  disinfectants.  Borax  might  be  used  for 
the  purpose,  but  it  is  expensive  ;  and  the  use  of  more  vigor- 
ous disinfectants  is  likely  to  make  the  material  poisonous 
to  hogs  subsequently  fed  upon  it,  or  to  dogs  who  very  fre- 
quently feed  upon  the  contents  of  the  garbage  receptacle. 
Such  disinfectants  are  quite  unnecessary,  and  the  only 
thing  that  the  housewife  needs  to  do  is  to  keep  the  garbage 
can  tolerably  clean,  and  to  see  that  it  is  emptied  as  fre- 
quently as  possible.  She  should  remember,  however,  that 
she  cannot  depend  upon  the  garbage  man  to  clean  the  recep- 
tacle. He  will  simply  empty  it.  If  the  garbage  can  gets 
to  smelling  offensively,  a  thorough  washing  with  hot  water 
and  sal  soda  applied  vigorously  with  an  old  broom  will  make 
a  great  improvement.  Naturally  greater  attention  must 
be  given  to  the  matter  in  the  summer  than  in  the  winter. 


138  BACTERIA,  YEASTS,  AND    MOLDS 

Closely  associated  with  these  problems  are  certain  other 
minor  questions  relating  to  the  kitchen  sink.  In  the 
ordinary  sink  a  considerable  amount  of  organic  material  is 
liable  to  find  its  way  into  the  drain  and  trap.  The  cloths 
used  for  washing  dishes  are  also  quite  sure  to  become 
soiled  with  various  forms  of  organic  material  from  the  food. 
These  materials  are  liable  to  bacterial  action  and  uierefore 
will  decay  and  become  offensive.  Consequently  boiling 
water  should  be  occasionally  poured  down  the  sink  drain 
to  disinfect  the  trap  as  far  as  possible,  and  the  cloths  used 
in  dishwashing  should  be  thoroughly  washed  in  boiling 
water  and  dried  to  prevent  them  from  becoming  offensive 
by  furnishing  a  chance  for  bacterial  growth. 


CHAPTER   X 
THE  PRESERVATION  OF  FOOD:  DRYING;   COOLING 

The  growth  of  bacteria  in  food  is  nearly  always  unde- 
sirable and  the  housewife  must  always  aim  to  prevent  it. 
Even  where  the  incipient  decomposition  products  are 
useful  because  pleasant  to  taste,  this  taste  is  developed 
in  the  food  before  it  is  received  into  the  house,  so  that 
the  housewife  is  not  concerned  in  the  methods  adopted 
to  produce  the  flavors.  Her  sole  aim  must  be  to  prevent 
the  food  from  spoiling.  To  do  this  she  must  constantly 
bear  in  mind  that  putrefaction  is  always  due  to  the  growth 
of  microorganisms,  and  that  all  types  of  putrefaction  and 
decay  may  be  prevented  by  stopping  the  growth  of  such 
organisms,  and  delayed  by  decreasing  its  rapidity.  Any- 
thing which  will  check  the  activity  of  bacterial  growth  will 
delay  the  spoiling  of  food  products.  In  order  to  know 
how  to  treat  food  for  this  purpose  it  is  most  useful  to 
bear  in  mind  the  facts  already  mentioned  in  regard  to  the 
growth  of  bacteria. 

To  the  housewife  of  to-day  the  problem  of  food  preser- 
vation is  of  less  significance  than  it  was  fifty  years  ago. 
To-day,  at  least  in  all  communities  of  even  moderate  size, 
these  problems  have  been  largely  solved  for  her  by  the 
marketman,  and  she  can  buy  her  food  in  such  small  quan- 
tities that  frequently  she  does  not  need  to  consider  the 
problem  of  preservation.  The  housekeeper  of  fifty  years 

139 


140  BACTERIA,  YEASTS,  AND    MOLDS 

ago  was  confronted  with  many  problems  in  the  preserva- 
tion of  meats,  vegetables,  and  fruits,  because  she  was 
likely  to  have  large  quantities  brought  to  her  hands  at 
once  for  immediate  disposal.  But  though  the  questions 
are  not  so  pressing  in  the  modern  home,  they  are  still  con- 
stantly arising  in  the  well-regulated  house.  A  somewhat 
extended  notice  of  the  subject  is  therefore  necessary. 

The  Use  of  Foods  while  Fresh.  The  first  thing  that 
must  always  be  borne  in  mind  is  that  nearly  all  kinds  of 
food  are  better  when  used  as  fresh  as  possible.  The 
earlier  food  is  consumed  after  it  reaches  the  household, 
the  surer  it  is  to  be  free  from  the  troublesome  action  of 
bacteria  and  the  more  certain  it  is  not  to  develop  decom- 
position tastes  and  flavors.  The  necessity  of  using  food 
while  fresh  is  much  more  imperative  with  some  foods 
than  with  others.  Meats  are  especially  liable  to  spoil,  the 
meat  of  immature  animals  more  quickly  than  that  of  adult 
animals,  and  must  be  used  promptly.  Many  fruits,  like 
cherries,  berries,  peaches,  and  pears,  keep  only  a  short 
time,  and  beans  and  peas  spoil  very  quickly  if  kept  moist. 
The  endeavor  should  always  be  to  use  such  materials 
at  once. 

The  housewife  in  our  modern  community  should  remem- 
ber that  a  small  proportion  of  the  food  she  buys  is  really 
fresh.  The  crowding  of  people  together  into  cities  de- 
mands a  food  supply  coming  from  long  distances,  and 
the  constantly  open  markets  twelve  months  in  the  year 
require  some  food  to  be  preserved  for  weeks  and  months 
before  use.  Hence  our  markets  are  filled  and  our  tables 
loaded  with  various  forms  of  preserved  foods  ;  and  whether 
she  buys  canned  or  salted  goods,  or  meats  or  poultry,  the 


PRESERVATION   BY   DRYING  141 

housewife  may  be  confident  that  some  device  for  preser- 
vation has  likely  been  used  in  their  preparation.  The 
modern  city  is  possible  only  because  we  have  learned 
methods  of  food  preservation. 

It  is  of  course  not  always  possible  to  use  all  kinds  of 
food  in  a  fresh  condition,  and  it  becomes  quite  necessary 
to  have  some  means  devised  for  their  preservation.  The 
means  adopted  for  preservation  are  always  to  subject  the 
food  to  conditions  unfavorable  for  bacteria  growth. 

DRYING 

Since  bacteria  require  a  considerable  quantity  of  water 
for  their  growth  and  multiplication,  they  will  not  develop 
at  all  in  foods  that  are  even  moderately  dry.  Molds  will 
grow  upon  a  food  that  has  only  a  small  amount  of  water, 
but  bacteria  require  from  25^  to  30^)  of  water  in  their 
foods  in  order  that  they  may  grow.  Molds  will  grow 
upon  damp  floors,  damp  cloth,  or  paper,  but  bacteria  can 
attack  these  materials  only  when  soaked  with  water. 

A  practical  application  of  this  fact  is  drying,  —  one  of 
the  most  widely  used  methods  of  preserving  food.  This  is 
adopted  by  nature  for  the  purpose  of  preserving  many 
food  products,  like  corn,  wheat,  oats,  rye,  etc.  Nature 
wants  to  keep  such  seeds  from  decaying  for  some  time, 
perhaps  during  the  winter  season,  in  order  that  they  may 
be  in  good  condition  for  the  growth  of  the  young  seedlings 
in  the  spring.  To  accomplish  this  the  seed,  when  it  ripens, 
is  deprived  of  its  moisture,  so  that  when  fully  ripe  and 
ready  to  be  shed  from  the  plant  it  has  become  a  dry, 
hard,  tough  mass,  forming  the  grain  of  wheat  or  corn,  or 


142 


BACTERIA,  YEASTS,  AND    MOLDS 


the  dry  pea  or  bean.  Such  a  food  material  is  beyond  the 
reach  of  bacterial  action,  and,  unless  these  grains  become 
subsequently  soaked  with  water,  they  are  protected  from 
decay  (Fig.  62).  Bacteria  grow  in  them  readily  enough  in 
the  spring  when  they  are  moistened  and  begin  to  sprout. 
This  drying  of  the  grains  protects  all  kinds  of  flours 
and  meals  made  from  them.  The  wheat  is  ground  into 

flour,  and  the  corn  into 
meal,  each  of  which  con- 
tains but  a  small  amount 
of  moisture,  far  too  little 
to  allow  bacteria  to  feed 
upon  the  material. 

RW       1      _-*&^        Flour  is  Perfectly  good 

food  for  bacteria,  and  if 
we  only  moisten  it  with 
water,  putrefaction  and 
decay  begin  in  a  short 
time;  but  as  it  is 
ordinarily  prepared  the 
amount  of  moisture  is  too  slight  for  bacteria.  The  same 
is  true  of  all  flours  or  meals  prepared  by  grinding  dried 
seeds  furnished  by  plants.  To  a  less  extent  the  same  is 
true  of  various  food  preparations  made  from  these  flours. 
In  making  bread  or  cake  dried  flour  is  mixed  with  water 
and  subsequently  baked.  The  mixing  of  the  flour  with 
water  brings  it  into  a  condition  for  bacterial  action,  but 
the  baking  dries  up  enough  of  the  water  to  preserve  it. 
If  the  baking  is  so  thorough  that  the  water  is  almost 
completely  driven  off,  as  in  the  case  of  dried  bisctiits,  or 
crackers  as  they  are  called  in  the  United  States,  the 


FIG.  62.  Showing  nature's  method  of 
preserving  seeds  by  drying.  The  upper 
figures  are  the  fresh  seed,  the  lower 
figures  the  same  after  drying  for  winter 
preservation. 


PRESERVATION   BY   DRYING  143 

material  is  left  so  completely  dry  that  bacteria  cannot 
consume  it  at  all.  Dried  crackers,  if  kept  dry,  can  be  pre- 
served indefinitely,  neither  decaying  nor  molding.  In  the 
case  of  bread  and  soft  cakes  the  water  is  not  wholly  driven 
off ;  hence  these  foods  are  not  protected  entirely  from 
the  action  of  microorganisms.  As  a  rule  bacteria  cannot 
attack  them  and  the  housewife  hardly  fears  their  decay; 
but  molds  can  grow  upon  them  readily,  and  they  must 
therefore  be  protected  by  means  already  suggested. 

In  addition  to  foods  that  are  naturally  dry,  a  large 
variety  of  others  may  be  preserved  completely  from  bac- 
terial action  by  artificial  drying.  This  method  of  pre- 
serving has  been  known  for  centuries  and  is  understood 
by  both  civilized  people  and  savages.  Most  kinds  of  meat 
can  be  treated  in  this  way,  and  the  drying  of  meat  is 
carried  on  to  a  large  extent  in  different  parts  of  the  world. 
The  frontiersman  and  the  hunter  in  the  woods  sometimes 
cut  the  flesh  of  deer,  bears,  and  other  animals  into  thin 
strips  and  hang  it  where  it  will  be  dried  by  the  heat  of  the 
sun.  This  dried  meat  is  called  pemmican,  a  tough,  hard, 
dry  substance  which  can  be  kept  for  months  without 
danger  of  decay.  It  is  good  food,  though  somewhat  less 
digestible  than  fresh  meat.  A  similar  drying  could' be 
adopted  in  the  household  to  preserve  meats,  but  it  is 
rarely  worth  while. 

Usually  the  efficacy  of  the  drying  is  increased  by  the 
use  of  salt.  This  plan  for  the  preservation  of  meat  is 
adopted  in  many  parts  of  the  world  where  cattle  are  plenty 
and  the  market  is  distant.  In  South  America  thousands  of 
tons  of  dried  flesh  are  prepared  each  year,  the  drying  in 
this  case  being  produced  artificially,  and  the  meat  being 


144  BACTERIA,   YEASTS,  AND   MOLDS 

still  further  protected  from-  decay  by  the  addition  of  a 
small  quantity  of  salt.  Such  preserved  meats  are  then 
shipped  all  over  the  world  and  form  an  excellent  food 
which  can  be  kept  indefinitely.  The  commercial  names 
under  which  this  dried  meat  is  sold  are  several ;  the  more 
common  ones  are  charque  and  tassajo.  Such  meats,  though 
useful,  do  not  take  the  place  of  the  fresh  product.  Their 
flavor  is  changed ;  they  are  tough  and  not  easy  to  digest. 
A  more  familiar  method  of  preserving  meat  is  the  cur- 
ing of  hams,  bacon,  etc.  In  such  cases  the  flesh  is  first 
salted  thoroughly  by  soaking  in  a  brine,  and  then  sub- 
jected to  the  action  of  smoke  from  burning  wood.  Such 
smoked  food  is  thoroughly  protected  from  bacterial  action 
by  at  least  three  factors  :  (i)  The  material  becomes  some- 
what dry,  so  that  the  bacteria  cannot  readily  act  upon  it. 

(2)  The  action  of  the  smoke  is  in  a  measure  antiseptic, 
partly  destroying  bacterial  life  upon  the  surface,  and  at  the 
same  time  so  impregnating  the  meat  with  injurious  vola- 
tile products  that  bacteria  cannot  ordinarily  grow  in  it. 

(3)  The  salt  is  itself  injurious  to  bacterial  life.     The  ham  is 
thus  preserved  from  the  action  of  bacteria  by  a  combina- 
tion of  drying,  smoking,  and  salting,  all  of  which  processes 
together  are  sufficient  to  prevent  completely  the  subse- 
quent growth  of  bacteria,  although  molds  may  grow  upon 
it  if  it  is  not  properly  protected.    The  same  thing  is  true  of 
dried  beef,  a  material  preserved  from  decay  partly  by  a  pre- 
liminary soaking  in  brine  and  partly  by  a  subsequent  drying. 
The  methods  of  preparing  dried  beef  vary.    Sometimes  the 
process  is  one  of  artificial  drying  simply,  but  commonly 
smoking  and  salting  are  adopted  to  aid  in  the  process.    The 
drying  of  flesh  is  sometimes  carried  out  so  completely  that 


PRESERVATION   BY   DRYING  145 

the  mass  can  be  reduced  to  a  powder.  Powdered  meat, 
however,  is  an  article  of  commerce  not  very  widely  used. 

Drying  is  adopted  extensively  for  a  variety  of  other 
animal  foods.  It  is  much  used  in  preserving  fish,  some- 
times without  salting,  sometimes  with  an  abundance  of 
salt.  The  heat  of  the  sun,  artificial  heat,  and  smoking 
are  all  employed.  Mussels  and  other  shellfish  are  some- 
times preserved  by  drying. 

One  of  the  most  recent  and  useful  applications  of  dry- 
ing is  in  evaporating  muk.  Milk  is  now  easily  dried  by 
special  devices  and  is  put  upon  the  market  at  a  low  price. 
The  dried  product  will  keep  indefinitely,  and  is  an  extremely 
valuable  food,  since  it  is  one  of  the  cheapest  as  well  as 
the  most  nutritious  that  can  be  bought.  It  will  not  take 
the  place  of  fresh  milk,  for  when  subsequently  dissolved 
in  water  it  has  a  peculiar  flavor,  not  unpleasant,  but  not 
like  milk.  For  baking  and  for  many  other  purposes,  how- 
ever, it  has  proved  to  be  one  of  the  most  useful  as  well  as 
one  of  the  cheapest  of  foods.  It  is  as  nutritious  as  milk, 
is  easily  digested,  and  has  the  great  advantage  of  keeping 
indefinitely  without  decaying,  souring,  or  molding. 

In  the  drying  of  flesh,  milk,  etc.,  it  must  be  remembered 
that  the  process  simply  checks  the  growth  of  bacteria,  but 
does  not  necessarily  kill  them.  Hence,  if  the  meat  con- 
tained any  disease  germs  at  the  time  of  drying,  the  process 
itself  would  not  remove  the  danger  of  eating  it.  Meat 
from  diseased  animals  cannot,  therefore,  be  rendered  fit 
to  eat  by  drying.  Even  the  parasitic  worm,  Trichina,  can 
withstand  the  smoking  in  the  curing  of  ham.  Unless  the 
temperature  is  raised  quite  high  during  the  drying,  the 
process  does  not,  therefore,  remove  dangers  attending 


146  BACTERIA,  YEASTS,  AND   MOLDS 

the  use  of  food  procured  from  diseased  animals.  In  the 
process  commonly  adopted  for  drying  milk,  sufficient  heat 
is  used  to  render  harmless  any  disease  germs  it  may  have 
originally  possessed. 

A  large  variety  si  fruits,  berries,  and  vegetables  are  also 
capable  of  preservation  indefinitely  by  the  simple  process 
of  drying.  The  farmer's  wife  has  long  known  that  she 
can  preserve  apples  by  cutting  them  into  small  pieces  and 
hanging  them  in  strings  over  her  kitchen  fire  to  dry.  The 
same  thing  is  possible  for  many  vegetables,  like  squashes, 
pumpkins,  and  even  potatoes.  Many  kinds  of  berries  — 
blackberries,  blueberries,  strawberries,  and  some  others 
—  can  be  preserved  by  merely  extracting  from  them  a 
large  part  of  their  water.  This  drying  of  fruits  and  vege- 
tables is  often  accomplished  by  subjecting  them  to  artificial 
heat,  but  more  commonly  in  recent  years  the  materials 
are  subjected  to  hydraulic  pressure,  by  means  of  which 
the  water  is  actually  squeezed  out.  A  slight  subsequent 
drying  is  then  sufficient  to  preserve  the  material  almost 
indefinitely. 

Some  fruits  are  preserved  by  a  combination  of  drying 
and  the  presence  of  considerable  sugar.  Raisins,  for 
example,  are  dried  grapes,  but  they  are  not  dried  so  com- 
pletely as  berries,  for  some  moisture  is  left  in  them.  The 
preservation  of  the  raisin  from  decay  is  due  in  part  to 
the  lack  of  water,  but  chiefly  to  the  presence  of  a  high 
per  cent  of  sugar,  which  is  in  itself  deleterious  to  bac- 
terial action.  So,  too,  with  other  sweet  fruits  like  prunes, 
apricots,  figs,  dates,  currants,  etc.  Their  preservation  is 
partly  a  matter  of  drying  and  partly  the  result  of  the 
sugar  present. 


PRESERVATION   BY   DRYING  147 

A  large  variety  of  fruits  may  be  preserved  by  drying 
if  we  only  have  proper  means  for  extracting  the  water. 
Indeed,  probably  any  fruit  could  be  thus  preserved  for 
future  use  if  we  could  find  a  practical  method  of  drying 
it.  To  do  this  the  fruit,  divided  into  small  pieces,  must 
be  subjected  to  a  heat  sufficient  to  dry  it  rapidly  so  as 
to  prevent  decay,  but  not  sufficient  to  cook  it.  It  is 
hardly  worth  while  to  attempt  such  work  in  the  ordinary 
home,  for  the  results  are  not  entirely  satisfactory,  and 
dried  fruits  are  easily  purchased.  Some  such  method  is 
practical  with  certain  fruits  and  impractical  with  others ; 
but  it  always  greatly  changes  the  nature  of  the  fruit. 
Before  it  can  be  used  the  dried  fruit  must  be  soaked 
with  water  to  soften  it,  after  which  it  rarely  bears  much 
resemblance  to  the  original  fruit.  Dried  apples  are  quite 
different  from  fresh ;  the  taste  of  the  fresh  apple  has  wholly 
disappeared,  leaving  in  its  place  an  entirely  different  flavor. 
The  same  is  true  of  practically  all  fruits  preserved  by  dry- 
ing. Their  food  value  has  not  been  reduced,  for  a  bit  of 
dried  apple  is  just  as  nutritious  as  the  fresh  ;  but  fruits 
have  very  little  food  value  at  any  time,  and  are  eaten 
mostly  for  their  flavors.  Dried  fruit  is  much  inferior  in 
taste  and  cannot  be  used  for  so  many  purposes  as  fresh 
fruit.  The  drying  of  fruits  and  vegetables  leaves  a  pulpy, 
somewhat  tasteless  substance,  which,  although  it  still 
retains  its  original  food  material,  has  lost  the  peculiar 
charm  which  gives  value  to  the  fresh  fruit. 

It  must  be  evident,  then,  that  drying  is  the  most  widely 
adopted  method  of  preserving  foods,  but  it  is  not  equally 
useful  for  all  kinds.  With  some  it  works  to  perfection. 
For  grains  or  other  foods  obtained  from  seeds  it  leaves 


148  BACTERIA,  YEASTS,  AND   MOLDS 

nothing  to  be  desired.  It  is  useful  for  meats  and  many 
other  kinds  of  animal  foods.  For  vegetables  and  fruits 
its  value  is  far  less,  and  sometimes  very  doubtful.  For 
them  it  should  be  used  only  where  there  is  a  large  quantity 
of  fresh  material  for  which  no  better  method  of  preserva- 
tion can  be  found. 


USE  OF  Low  TEMPERATURES 

The  value  of  low  temperatures  in  preserving  all  forms 
of  food  is  familiar  to  every  one.  Microorganisms  are 
stimulated  into  active  growth  by  high  temperatures  and 
checked  by  low  temperatures.  It  must  be  remembered, 
however,  that  the  temperature  at  which  bacteria  grow 
most  readily  is  not  always  the  same ;  for  although  some 
species  flourish  only  at  warm  temperatures,  from  70°  to 
1 00°,  others  grow  best  at  temperatures  only  a  few  degrees 
above  freezing.  While,  then,  a  low  temperature  will  check 
the  development  of  most  bacteria,  it  will  not,  unless  it 
is  actually  below  freezing,  wholly  prevent  it,  since  some 
species  grow  readily  enough  at  low  temperatures.  In  the 
consideration  of  the  use  of  low  temperatures,  therefore, 
three  phases  of  the  subject  may  be  considered,  based 
upon  the  degree  of  cold  obtained. 

i.  Cold  Storage.  By  cold  storage  is  meant  the  use  of 
storehouses  which  are  cooled  artificially,  and  where  a  very 
low  and  constant  temperature  is  maintained  for  months 
at  a  time.  In  some  compartments  the  temperature  is 
held  at  a  few  degrees  above  freezing,  while  in  others 
it  is  even  below  freezing.  These  low  temperatures  are 
commonly  produced  by  the  use  of  artificial-ice  machines, 


COLD   STORAGE  149 

based  upon  the  vaporization  of  ammonia,  and  kept  con- 
stant in  spite  of  great  changes  in  the  temperature  of  the 
air  outside.  Cold-storage  plants  are  a  modern  device, 
and  only  within  comparatively  recent  years  have  they 
come  to  be  used  to  any  considerable  extent  for  the  pres- 
ervation of  food.  They  are  now  found  in  all  our  large 
cities,  and  they  are  being  utilized  more  and  more  each 
year,  producing  profound  modifications  of  the  conditions 
of  civilized  life.  By  means  of  them  a  large  variety  of 
foods  can  be  preserved  for  many  months  without  any 
tendency  toward  putrefaction  and  decay,  and  may  be  used 
at  any  time  with  the  confidence  that  they  have  been  kept 
in  a  perfectly  good  condition.  The  cold-storage  plants 
make  it  possible  to  keep  fresh  for  winter  or  spring  use  a 
large  quantity  of  the  perishable  products  which  previously, 
if  not  capable  of  preservation  by  canning,  it  was  necessary 
to  throw  away  because  of  the  certainty  of  putrefaction  and 
decay.  Such  devices  are  producing  a  far  more  equitable 
condition  in  the  food  supply  of  modern  communities.  It 
is  now  possible  to  have  fresh  at  any  season  of  the  year 
the  perishable  food  products  produced  at  almost  any  other 
season,  provided  we  take  the  trouble  to  preserve  them  in 
cold-storage  plants,  and  our  city  markets  can  furnish  fresh 
fruits  at  almost  any  time. 

The  length  of  time  during  which  food  can  be  preserved 
by  cold  storage  depends  upon  the  temperature.  If  actually 
frozen,  as  is  commonly  the  case  with  fish,  fowl,  and  flesh 
generally,  food  may  be  preserved  indefinitely.  Frozen 
food  in  the  arctic  regions  keeps  for  years,  and  will  indeed 
keep  as  long  as  it  remains  frozen.  The  same  would  be 
true  of  frozen  food  in  cold  storage.  But  some  kinds  of 


150  BACTERIA,   YEASTS,  AND    MOLDS 

food,  particularly  fruits,  are  ruined  by  freezing.  In  these 
cases  the  temperature  may  approach  freezing  but  must 
never  quite  reach  it.  Such  food  will  be  preserved  for  a 
while,  perhaps  for  months  if  the  temperature  is  low,  but 
not  indefinitely. 

The  cold-storage  plant  cannot  be  utilized  by  the  house- 
wife, and  need  not  therefore  be  further  considered  here. 
She  should  always  remember,  however,  that  during  the 
winter  and  spring  a  considerable  part  of  the  perishable 
food  products  purchased  in  markets  has  come  from  cold- 
storage  plants,  where  they  have  been  retained  for  a  long 
period  at  a  temperature  in  the  vicinity  of  freezing,  or  even 
below  it.  If  she  buys  fish,  fowl,  or  fruit  during  the  win- 
ter, in  a  city  market,  she  may  regard  it  as  probable  that 
they  have  come  from  cold  storage.  This  is  a  matter  of 
considerable  importance  because  of  the  practical  question 
of  the  keeping  property  of  such  material. 

The  question  has  frequently  been  raised  whether  foods 
from  cold  storage  is  not  subject  to  exceptionally  rapid 
decay  after  being  brought  again  to  a  warm  temperature. 
It  is  a  general  belief  that  meats  and  other  materials  that 
have  been  frozen  decay  very  rapidly  after  they  are  thawed 
out,  and  hence  that  food  taken  from  cold  storage  must 
be  used  quickly,  since  it  will  putrefy  more  rapidly  than 
when  fresh.  This  belief  seems  to  be  well  founded,  but 
the  reason  for  it  is  not  clear.  Possibly  the  food  is  slightly 
changed  in  its  physical  nature  by  the  freezing  so  that 
bacteria  can  more  readily  act  upon  it  when  it  is  thawed. 
In  many  cases,  however,  especially  with  fruits,  which  are 
not  actually  frozen,  the  rapid  decay  which  follows  re- 
moval from  cold  storage  is  due  to  the  large  amount  of 


THE   ICE   CHEST  151 

moisture  which  condenses  upon  the  surface  of  the  cold 
fruit  when  it  is  placed  in  warm  or  damp  air.  Such  sur- 
face moisture,  as  we  have  seen,  furnishes  the  necessary 
condition  for  the  starting  of  mold  growth.  The  prac- 
tical lesson  to  be  learned  is  that  after  the  material  has 
been  removed  from  the  cold  storage  and  warmed  up  to 
ordinary  room  temperatures  it  should  be  consumed  as 
rapidly  as  possible,  because  putrefaction  and  decay  are 
sure  to  take  place  speedily.  If  not  used  at  once,  it  must 
be  kept  in  an  ice  chest.  There  is  practically  as  much 
difficulty  in  keeping  food  bought  in  the  markets  from 
decay  in  the  winter,  if  kept  in  a  warm  house,  as  there 
is  in  the  summer. 

Cold-storage  plants  are  hardly  found  outside  of  large 
cities,  and  persons  at  a  distance  must  depend  upon  other 
means  of  producing  low  temperatures.  These  are  easy 
to  obtain  in  winter,  but  difficult  in  summer. 

2.  Temperature  of  an  Ice  Chest.  A  far  less  efficient 
means  of  obtaining  low  temperature  is  by  the  use  of  the 
ordinary  ice  chest, — less  efficient  than  cold  storage  simply 
because  the  temperature  is  higher.  The  temperature  of 
ice  chests  is  variable,  depending  upon  the  size  of  the  chest 
and  the  amount  of  ice  in  it.  It  will  sometimes  be  as  low 
as  40°,  or  even  lower,  but  never  quite  reaches  the  freezing 
point ;  at  other  times  it  will  run  up  to  50°,  and  as  the  ice 
melts  the  temperature  rises  to  that  of  the  outer  air.  Food 
preserved  in  an  ice  chest  is  far  less  thoroughly  protected 
than  in  cold-storage  plants.  The  use  of  the  ice  chest  is 
simply  a  means  of  checking  the  development  of  bacteria, 
but  it  by  no  means  stops  their  growth.  At  the  tem- 
perature of  40°  most  bacteria,  if  they  grow  at  all,  grow 


152  BACTERIA,  YEASTS,  AND    MOLDS 

very  slowly,  and  the  food  may  therefore  be  preserved  for 
quite  a  long  period,  although  it  is  sure  in  the  end  to 
undergo  certain  forms  of  putrefaction. 

The  type  of  putrefaction  that  occurs  in  material  kept 
in  an  ice  chest  is  usually  somewhat  different  from  that 
which  occurs  in  the  same  material  at  an  ordinary  room 
temperature.  The  common  putrefactive  bacteria  grow 
readily  at  high  temperatures,  but  hardly  at  all  at  the 
temperature  of  the  ice  chest.  Other  types  of  bacteria, 
however,  grow  more  readily  at  the  lower  than  at  the 
higher  temperatures,  and  meat  or  other  food  kept  in  the 
refrigerator  will  in  the  course  of  time  undergo  a  type 
of  decay  due  to  the  microorganisms  favored  by  the  low 
temperature.  This  decayed  meat  appears  somewhat  dif- 
ferent from  decayed  meat  at  higher  temperatures  and  has 
a  different  odor, — a  fact  indicating  a  different  type  of  pu- 
trefaction. Certain  peculiar  kinds  of  decay  are  seen  at 
these  low  temperatures  which  are  hardly  found  under 
other  conditions.  Occasionally,  for  example,  fleshy  foods, 
particularly  those  from  salt  water,  like  lobsters  or  fish, 
develop  a  peculiar  phosphorescence  if  kept  in  an  ice  chest. 
If  examined  in  the  dark  they  will  be  seen  to  glow  with  a 
somewhat  brilliant  greenish  light.  This  phosphorescence 
is  due  to  the  development  of  certain  very  interesting  kinds 
of  bacteria,  and  always  appears  if  they  grow  luxuriantly 
at  low  temperatures.  They  grow  chiefly  upon  foods  which 
contain  considerable  salt,  and  hence  particularly  in  marine 
foods.  They  are  more  likely  to  be  found  in  meat  pre- 
served in  an  ice  chest,  since  the  more  common  decay 
produced  by  other  bacteria  will  at  higher  temperatures 
mask  the  growth  of  the  phosphorescent  bacteria.  It  is 


THE    ICE   CHEST  153 

not  necessary  to  throw  such  food  away,  since  the  phos- 
phorescence does  not  appear  to  r,encler  it  unwholesome, 
and  it  may  be  eaten  with  impunity. 

Although  far  less  efficient  than  cold  storage,  the  ice 
chest  is  a  means  of  preserving  for  a  short  time  food  that 
would  otherwise  quickly  spoil.  Its  efficiency  depends 
upon  its  temperature.  The  larger  the  amount  of  ice  in 
an  ice  chest  the  lower  its  temperature  and  the  greater  its 
efficiency.  If  the  amount  of  ice  is  very  small  there  will 
be  such  a  rise  in  the  temperature  that  food  placed  in  the 
ice  chest  will  spoil.  In  spite  of  its  drawbacks  the  ice  chest 
has  become  a  necessity  in  the  well-ordered  household.  It 
is  frequently  necessary  to  preserve  foods  for  a  few  hours 
before  they  can  be  used,  and  in  the  warmer  temperature 
of  spring,  summer,  or  autumn  this  is  frequently  impos- 
sible without  the  use  of  ice.  In  particular  is  this  true  of 
the  preservation  of  milk,  a  topic  .vhich  we  shall  notice 
by  itself. 

In  many  parts  of  America  the  ice  chest  has  become  an 
almost  universal  aid  in  the  housekeeping  of  families  in 
moderate  circumstances,  and  has  greatly  simplified  prob- 
lems of  home  economics.  To  the  poorer  families,  how- 
ever, it  is  hardly  known.  The  home  with  an  ice  chest 
may  purchase  food  to  advantage  in  quantity  and  preserve 
it  for  a  few  days  till  used.  The  poorer  families  must  rely 
upon  their  food  being  preserved  by  dealers  in  food  sup- 
plies, and  can  therefore  buy  only  such  small  quantities  as 
can  be  used  at  once. 

To  keep  an  ice  chest  in  good  condition  it  must  be 
frequently  cleaned.  The  inside  is  sure  to  be  damp,  and 
dirt  is  quite  likely  to  collect  in  the  cracks  and  corners. 


154  BACTERIA,  YEASTS,  AND   MOLDS 

This  dirt  will  furnish  a  good  place  for  the  growth  of  such 
bacteria  as  thrive  in  low  temperatures,  and  thus  the  ice 
chest  in  time  becomes  unfit  for  use.  Food  will  not  keep 
well  under  such  conditions,  becoming  infected  with  bac- 
teria as  well  as  affected  by  the  odors  given  off  from 
the  decaying  material.  A  frequent  cleaning  is  necessary 
to  keep  the  ice  chest  sweet  and  thus  make  it  possible  to 
preserve  food  properly. 

3.  Temperature  of  a  Cool  Cellar.  —  It  sometimes  hap- 
pens that  the  only  place  for  storing  the  autumn  products 
is  a  cool  cellar.  This  is  frequently  the  case  on  the  farm, 
especially  when  considerable  material  is  to  be  preserved. 
A  cool  cellar  is  of  use  in  any  home,  for  it  makes  possible 
the  purchasing  of  fruits  and  vegetables  in  bulk  during  the 
fall,  when  they  are  cheap,  and  their  preservation  for  use 
till  a  later  season  when  they  are  more  expensive. 

The  value  of  a  cool  cellar  rests  upon  two  facts  :  (i)  The 
temperature  is  usually  lower  than  in  other  parts  of  the 
house.  (2)  It  is  more  likely  to  be  uniform.  A  cellar  under- 
neath a  house  will  have  during  the  winter  season,  at  least 
in  cool  climates,  a  temperature  not  much  above  freez- 
ing. For  reasons  which  we  have  already  considered  such  a 
temperature  will  preserve  fruits  and  vegetables  from  bac- 
terial action  or  other  types  of  decay.  Where  such  a  cellar 
is  at  hand  it  is,  therefore,  very  well  adapted  to  the  preser- 
vation of  fruits.  Any  other  room,  if  its  temperature  could 
be  controlled,  would  be  just  as  good,  and  if  it  were  light 
would  be  somewhat  better  than  a  cellar,  which  is  usually 
dark.  But  rooms  above  ground  are  generally  lighted  by 
windows,  which  make  it  difficult  to  control  the  tempera- 
ture. In  the  winter  such  rooms  are  pretty  sure  to  have 


THE   COOL   CELLAR  155 

a  temperature  below  freezing  in  the  cold  climates,  and 
this  is  sufficient  to  ruin  fruits,  most  of  which  are  spoiled 
by  freezing. 

Since  the  value  of  the  cellar  in  preserving  fruits  and 
vegetables  is  simply  in  its  uniform  and  low  temperature, 
the  lower  the  temperature  —  provided  it  is  above  freez- 
ing—  and  the  more  even  it  is,  the  more  satisfactory  are 
the  results.  On  the  other  hand,  a  warm  cellar,  so  char- 
acteristic-of  most  modern  houses  heated  by  furnaces,  is 
of  very  little  use  in  preserving  foods,  for  decay  occurs 
about  as  rapidly  in  such  a  cellar  as  it  would  elsewhere  in 
the  house,  more  rapidly,  indeed,  than  in  a  cold  pantry. 
Since  one  can  purchase  large  quantities  of  many  foods 
more  reasonably  in  the  fall  by  taking  advantage  of  the 
low  market  rates,  it  is  economy  to  have  a  compartment 
partitioned  off  from  the  heating  apparatus  in  the  cellar 
where  fruits  and  vegetables  can  be  stored.  A  cold  closet 
is,  indeed,  almost  necessary  for  the  keeping  of  preserves. 

In  the  use  of  a  cold  cellar  to  preserve  vegetables  it  is 
well  to  bear  in  mind  that  many  of  them  —  parsnips,  car- 
rots, beets,  turnips  —  are  better  preserved  if  buried  in 
sand,  and  that  fruits  keep  better  in  sawdust,  oat  chaff,  or 
some  other  material  which  absorbs  moisture. 

Other  Devices.  Any  device  for  cooling  will  of  course 
be  useful  in  preserving  foods.  Cold  running  water,  spring 
houses,  submerging  in  iced  water,  are  all  used  for  the  pur- 
pose. Suspension  in  deep  wells  is  one  of  the  most  com- 
mon methods  of  obtaining  a  low  temperature  for  milk, 
butter,  etc.,  and  is  widely  adopted  in  houses  where  ice  is 
not  at  hand.  Even  the  scheme  of  packing  material  in 
damp  leaves  may  be  of  some  value,  since  the  evaporation 


156  BACTERIA,   YEASTS,  AND    MOLDS 

of  the  water  from  the  leaves  lowers  the  temperature.  In 
warm  climates  this  principle  is  made  use  of  to  cool  drinks 
by  keeping  them  in  earthenware  receptacles  the  surfaces 
of  which  are  constantly  moistened.  The  evaporation  of 
the  water  on  the  outside  cools  the  inclosed  liquids. 

Cooling  may  be  used  for  any  kind  of  food.  Three 
general  rules  should  always  be  followed  where  food  is 
put  aside  for  preservation  at  a  low  temperature. 

1.  Cool  the  food  as  quickly  as  possible.     This  should 
be  done  before  covering  and  setting  aside  for  keeping. 

2.  Use  every  possible  device  for  avoiding  moisture. 

3.  Use  food  quickly  after  taking  it  from  its  place  of 
storing,  for  such  food  when  warmed  decays  rapidly. 

THE  USE  OF  HEAT 

The  easy  destruction  of  bacteria  by  heat  suggests  a 
means  for  increasing  the  keeping  properties  of  many 
foods.  Liquid  foods  may  first  be  boiled  and  then  cooled 
as  quickly  as  possible,  after  which  they  may  be  put  away 
in  cold  places  for  preservation.  It  is  necessary  that  the 
material  should  actually  be  boiled,  since  a  lower  tempera- 
ture is  not  only  useless  but  frequently  detrimental.  If  a 
putrescible  material  is  simply  steeped  in  warm  water  and 
then  put  away,  it  will  spoil  rapidly ;  if  it  is  boiled  it  may 
be  preserved  for  some  time.  Boiling  is  useful  for  such 
materials  as  soups,  stews,  or  any  liquid  not  injured  by 
boiling.  It  must  be  remembered,  however,  that  boiling 
will  not  preserve  the  material  indefinitely ;  it  simply  delays 
the  spoiling. 


CHAPTER    XI 

THE    USE    OF    PRESERVATIVES 

In  early  years  the  only  means  adopted  for  preserving 
food  were  drying  and  cooling,  both  of  which  have  been 
known  and  used  for  many  centuries.  Within  the  last 
fifty  years  other  methods  have  been  used  for  the  same 
purpose,  and  for  some  kinds  of  food  they  are  far  more 
satisfactory  and  valuable  than  those  just  mentioned.  The 
first  which  we  shall  notice  is  the  use  of  preservatives. 

The  explanation  of  using  preservatives  is  that  it  adds 
to  the  food  something  which  will  check  the  growth  of 
microorganisms  and  thus  prevent  decay.  Such  preserv- 
atives must  fulfill  two  conditions  :  (i)  They  must  have 
some  antiseptic  power.  (2)  They  must  be  comparatively 
harmless  to  man. 

POISONOUS  PRESERVATIVES 

Since  we  know  that  the  spoiling  of  food  is  due  to  the 
growth  of  microorganisms  it  is  easy  to  find  chemical  sub- 
stances which  will  be  perfect  preservatives.  If  it  were 
simply  a  matter  of  protecting  food  from  decay,  it  would 
be  the  easiest  thing  in  the  world  to  bring  about  the 
result.  But  it  chances  that  most  of  the  materials  fatal 
to  the  life  and  growth  of  microorganisms  are  also  poison- 
ous to  man  and  therefore  cannot  be  used  in  his  foods. 


158  BACTERIA,   YEASTS,  AND    MOLDS 

This  greatly  restricts  the  number  of  materials  that  can  be 
used  for  food  preservation.  Some  it  is  quite  impossible 
to  use  because  of  their  violently  poisonous  nature.  For 
example,  carbolic  acid  and  corrosive  sublimate  will  preserve 
food  perfectly,  since  they  are  fatal  to  bacterial  growth  ; 
but  they  are  also  violent  poisons  to  man  and  hence  must 
not  be  put  in  his  foods.  There  are  other  chemicals,  how- 
ever, of  a  less  poisonous  nature  which  are  frequently  used 
for  the  preservation  of  foods. 

The  milder  drugs  in  use  to-day  for  this  purpose  are 
chiefly  borax,  benzoic  acid,  salicylic  acid,  and  formalin. 
Although  these  substances  are  poisonous  and  injurious 
to  man  when  used  in  considerable  quantity,  they  may  be 
swallowed  in  small  quantities  without  any  appreciable 
effect  upon  the  individual.  But  even  in  small  quantities 
they  have  the  power  of  checking  the  growth  of  bacteria, 
and  they  are  frequently  used  for  protecting  various  kinds 
of  food  from  the  spoiling  that  would  otherwise  occur. 

These  materials,  put  up  into  proper  form  for  use,  can 
be  found  in  our  markets  under  a  variety  of  commercial 
names.  They  usually  go  under  special  trade  names,  — pre- 
servaline,  fruit  preservaline,  antifermentine,  freezine,  etc. 
These  various  commercial  products  differ  in  their  chem- 
ical analyses,  but  are  all  made  up  of  mildly  poisonous 
materials.  No  two  of  these  preservatives  are  exactly 
alike,  but  most  of  them  are  made  up,  wholly  or  in  part,  of 
the  chemical  substances  above  mentioned.  The  preserva- 
line products,  for  example,  are  largely  borax,  while  the 
basis  of  freezine  is  formalin.  They  are  undoubtedly  effi- 
cient in  protecting  food  from  putrefaction  and  decay,  for 
they  all  check  bacteria  growth.  If  used  in  sufficient 


COMMERCIAL   PRESERVATIVES  159 

quantity  they  will  wholly  prevent  putrefaction,  and  even 
in  small  quantities  they  may  so  check  the  growth  as  to  pre- 
serve the  food  much  longer  than  usual.  For  this  reason 
they  are  extremely  convenient  and  have  been  widely  used 
by  people  who  do  not  understand  what  they  are.  Some 
have  found  them  so  convenient  that  they  have  given  up 
the  use  of  the  refrigerator  or  other  devices  for  producing 
cool  temperatures,  feeling  that  it  is  much  cheaper,  as  well 
as  more  convenient  and  more  satisfactory,  to  keep  their 
food  by  adding  a  small  quantity  of  preservaline  or  similar 
substance,  than  to  use  ice.  The  various  forms  of  pre- 
servatives may  be  used  for  almost  any  kind  of  food,  — for 
canning  fruits  or  vegetables,  for  preserving  milk,  meat, 
etc., —  and,  so  far  as  concerns  the  actual  protection  of  food 
from  decay,  they  certainly  accomplish  their  purpose. 

But  the  important  question  arises  whether  it  is  health- 
ful to  use  such  materials  in  our  food.  Every  one  of  them 
is  of  a  more  or  less  injurious  nature,  and  if  taken  into  the 
body  in  any  considerable  amount  will  produce  poisonous 
effects.  This  has  led  to  much  experimenting  and  discus- 
sion. In  past  years  a  considerable  portion  of  the  food 
products  on  the  market  has  been  treated  with  some  of  these 
food  preservatives,  —  borax  being  widely  used  for  this  pur- 
pose. In  the  markets  of  Europe  some  of  these  substances 
are  used  to  preserve  a  large  part  of  the  meats,  butter,  milk, 
etc.  England  obtains  great  quantities  of  her  provisions 
from  America  and  even  Australia,  and  it  seems  difficult, 
or  impossible,  to  deliver  them  at  such  long  distances  with- 
out treating  them  with  preservatives.  At  all  events,  the 
foods  coming  from  Australia  to  the  markets  of  England 
are  usually  so  treated.  The  use  of  preservatives  in  our 


l6o  BACTERIA,  YEASTS,  AND   MOLDS 

own  country  is  less  common,  because  our  markets  are  nearer 
the  sources  of  supply.  The  national  Pure  Food  Law, 
making  these  preservatives  illegal,  has  greatly  reduced 
their  use,  and  to-day  the  food  on  our  markets  is  mostly 
free  from  them. 

It  has  been  an  open  question  for  some  years  whether 
borax  used  in  small  quantities  under  such  conditions  is 
injurious  to  the  consumer.  Nor  is  the  question  yet  posi- 
tively settled.  It  has  become  in  a  measure  an  interna- 
tional question,  involving  the  importation  of  American  beef 
and  other  products  into  foreign  markets,  and  a  great  deal 
of  contradictory  evidence  has  been  advanced.  The  fact  that 
people  have  for  years  been  unconsciously  using  food  preserved 
by  means  of  such  substances,  without  any  apparent  injuri- 
ous effects,  seems  prima  facie  evidence  that  no  harm  results  ; 
but  it  is  possible,  of  course,  to  say  that  the  harmful  effects 
are  not  at  first  discernible,  and  that  many  of  the  digestive 
and  other  troubles  of  man  are  due  to  this  unconscious  con- 
sumption of  such  drugs.  No  positive  answer  can  be  given 
to  the  question.  Although  it  is  certain  that  many  people  in 
large  cities  have  occasionally,  or  even  constantly,  consumed 
them  without  any  apparent  injury,  the  general  belief  is  that 
they  are  injurious. 

Moreover,  when  such  materials  are  used  for  preserving 
food,  it  frequently  happens  that  a  considerable  quantity 
is  unconsciously  used.  Our  foods  usually  pass  through 
the  hands  of  several  people  before  they  are  consumed. 
The  original  producer  may  put  in  a  little  preservative,  the 
middleman  adds  more  in  order  that  the  material  may  not 
spoil  on  his  hands,  and  the  householder,  in  ignorance  of 
these  additions,  may  put  in  a  little  more.  By  the  time  it 


PRESERVATIVES   IN   FOOD  l6l 

reaches  the  table  it  may  be  so  filled  with  some  of  these 
poisonous  articles  as  to  be  decidedly  unwholesome.  In- 
stances are  known  where  violent  sickness,  and  even  death, 
especially  among  children,  has  been  traced  to  the  use  of 
such  preservatives,  which  had  been  added  by  one  person 
and  another  until  the  food  contained  them  in  large  quan- 
tity. This  is  particularly  true  of  milk,  because  it  spoils 
so  easily  and  quickly. 

For  these  various  reasons  the  use  of  such  preservatives  is 
to-day  forbidden  by  law  in  any  food  materials  offered  for  sale,1 
and  they  must  also  be  condemned  in  the  house,  since  even 
in  small  quantities  it  is  possible  that  their  daily  use  may 
cause  trouble.  It  is  also  quite  certain  that  if  a  preservative 
is  used  at  all,  the  food  will  occasionally  contain  so  much  of 
it  as  to  be  decidedly  unwholesome,  disastrous,  or  perhaps 
even  fatal.  No  housewife  should  therefore  depend  upon  any 
of  these  forms  of  preservation  for  her  food.  They  are  un- 
wholesome and  even  dangerous,  and  their  use  is  liable 
to  be  followed  by  ill  health  and  possibly  by  fatal  sickness. 
Particularly  should  it  be  understood  that  it  is  dangerous 
to  add  preservatives  to  food  that  has  previously  passed 
through  the  hands  of  others  who  may  have  already  used 
preservatives,  —  a  condition  of  things  especially  likely  to 
occur  with  milk.  Nothing  but  universal  condemnation 
for  the  use  of  the  commercial  materials  can  be  given  the 
householder.  If  any  preservative  is  to  be  used,  it  is  far 
cheaper  and  better  to  buy  pure  borax  from  the  druggist. 
For  milk  or  cream  this  may  be  used  in  the  proportion 
of  one  quarter  to  one  half  ounce  to  six  quarts  of  milk  or 

1  By  a  recent  ruling  a  small  amount  of  benzoic  acid  is  allowed  in  certain 
foods. 


162  BACTERIA,  YEASTS,  AND    MOLDS 

cream  ;  for  preventing  hams  or  bacon  from  molding  or 
becoming  slimy,  the  borax  may  be  dusted  on  the  surface, 
not  more  than  one  quarter  of  an  ounce  being  used  for 
each  pound  of  meat. 

But  any  one  of  these  materials,  if  used  in  considerable 
quantity,  is  certainly  injurious,  and  this  fact  makes  it 
quite  out  of  the  question  to  recommend  them  for  home 
use.  It  is  quite  impossible  for  the  physician,  much  less 
the  housewife,  to  know  how  much  may  be  used  without 
danger. 

NONPOISONOUS  PRESERVATIVES 

In  protecting  food  by  preservatives  we  are  not  confined 
to  poisons,  since  there  are  a  few  materials  capable  of  pre- 
serving food  that  are  not  poisonous  but  are,  on  the  con- 
trary, beneficial  to  us.  The  use  of  such  preservatives  is 
of  course  perfectly  proper.  Some  of  them  have  been  in 
use  for  many  years  and  at  the  present  time  are  more  used 
than  ever.  The  chief  ones  are  mentioned  below. 

Sugar.  As  already  indicated,  bacteria  do  not  grow 
readily  in  pure  sugar  solutions,  and  if  the  solutions  are 
very  strong  they  do  not  grow  at  all.  The  other  forms  of 
microorganisms  also,  molds  and  even  yeasts,  fail  to  grow 
readily  in  solutions  containing  a  considerable  quantity  of 
sugar.  It  is  therefore  quite  feasible  to  preserve  many 
of  our  foods  from  putrefaction  by  simply  mixing  them 
with  a  considerable  quantity  of  sugar.  Since  sugar  is  an 
excellent  food  for  man  it  does  not  injure  the  material  but 
increases  the  food  value  of  the  product.  As  a  preserva- 
tive sugar  has  more  value  against  bacteria  and  molds  than 
against  yeast.  It  is  the  material  which  readily  supports 


SUGAR  AS   A  PRESERVATIVE  163 

yeast  life,  and  it  occasionally  happens  that  materials  pre- 
served by  it  will  ferment.  But  this  does  not  commonly 
occur  if  the  percentage  of  sugar  is  high,  i.e.  40^6  to  50^. 

The  use  of  sugar  as  a  preservative  is  adopted  in  a 
number  of  well-known  products.  Fresh  fish  is  occasion- 
ally preserved  by  rubbing  with  sugar.  Condensed  milk  is 
preserved  by  the  addition  of  30^  to  40^  of  it.  It  changes 
the  nature  of  the  milk,  rendering  it  somewhat  less  digest- 
ible, but  does  not  materially  injure  it  as  a  food  product. 
Jellies  are  also  preserved  from  bacterial  action,  though 
not  wholly  from  fermentation,  by  the  large  amount  of  sugar 
which  they  contain ;  for  decay  would  take  place  quickly 
if  it  were  not  present.  It  has  been  used  for  a  long  time 
to  protect  fruits,  in  making  what  are  known  as  preserves. 
Almost  any  kind  of  fruit  may  be  preserved  by  stewing  it 
with  a  large  amount  of  sugar,  equal  parts  by  weight  of  fruit 
and  sugar  being  commonly  used.  At  a  moderate  heat  the 
fruit  is  so  thoroughly  impregnated  with  the  preservative 
that  no  putrefactive  organisms  are  subsequently  able  to 
grow  in  it,  and  it  may  then  be  preserved  almost  indefinitely. 
Marmalades  are  also  preserved  by  the  same  preservative. 
This  is  also,  in  a  measure,  as  we  have  seen,  the  reason  for 
the  preservation  of  raisins,  figs,  flhtms,etc.,  which  are  pre- 
served partly  by  drying  and  partly  by  the  presence  of  sugar. 
In  these  cases  the  fresh  fruit  contains  so  much  of  it  that 
none  is  artificially  added.  But  most  fruits  contain  too 
little  to  be  preserved  without  the  special  treatment  above 
described.  There  are  of  course  decided  limitations  to  the 
use  of  sugar  for  this  purpose,  for  the  flavors  of  most  of  our 
fruits  are  changed  when  mixed  with  a  great  deal  of  it. 
They  cease  to  have  fruit  flavors  and  become  a  sort  of 


164  BACTERIA,   YEASTS,  AND   MOLDS 

candied  material  which  can  be  used  only  as  a  sweetmeat 
or  a  sauce.  This  method  of  preservation  is  used  to-day 
much  less  than  in  earlier  years  before  the  wide  extension 
of  the  process  of  canning. 

Salt.  A  more  common,  harmless  preservative  is  salt. 
Materials  thoroughly  salted  are  completely  protected  from 
bacterial  growth.  Since  salt  is  harmless  and,  indeed,  a 
necessary  ingredient  in  our  food,  such  a  method  of  pre- 
serving is  quite  legitimate.  Salt  is  used  as  a  preservative 
for  a  variety  of  food  products.  Fat  pork  is  very  easily  pre- 
served by  keeping  it  immersed  in  a  strong  salt  solution 
called  brine,  producing  what  is  known  as  salt  pork.  Corned 
beef  and  corned  bacon  are  also  preserved  in  the  same  way. 
Cheeses  are  sometimes  preserved  in  brine,  and  the  same  is 
true  of  eggs.  In  other  cases  the  salt  is  mixed  with  the  food. 
Hams  and  some  other  meats  are  preserved  partly  by  salt- 
ing, and  in  most  forms  of  dried  beef  salt  is  added  to  assist 
in  the  preserving.  It  is  used  for  the  preservation  of  great 
quantities  of  fish,  particularly  marine  fish,  which  may  in 
this  way  be  preserved  indefinitely  from  bacterial  action. 
Fresh-water  fish  could  be  preserved  equally  well,  but  since 
they  are  not  generally  caught  in  large  numbers  they  are 
rarely  salted.  The  salting  of  butter  is  a  procedure  adopted 
partly  for  the  purpose  of  giving  a  salty  flavor  and  partly 
for  the  purpose  of  its  preservation.  In  the  preparation  of 
cheeses  salt  is  almost  always  used,  for  after  their  manufac- 
ture they  are  usually  kept  for  weeks  or  months  before  they 
are  ready  for  market,  and  salt  is  rubbed  into  their  surfaces 
to  prevent  the  growth  of  undesirable  microorganisms. 

It  must  be  remembered  that,  while  salting  preserves  the 
material  from  decay,  it  does  not  preserve  its  fresh  form. 


SALT   AS  A   PRESERVATIVE  165 

The  flavor  is  much  changed,  and  too  large  a  quantity  of 
salt  meat  is  not  wholesome.  Moreover,  salt  somewhat 
changes  the  physical  nature  of  food,  so  that  it  is  not 
quite  so  easily  digested.  Salt  foods,  therefore,  cannot 
wholly  take  the  place  of  fresh  foods.  Experience  has 
shown  that  when  used  in  large  quantities  and  unaccom- 
panied by  plenty  of  fresh  food  they  give  rise  to  a  kind 
of  digestive  derangement  known  as  scurvy,  a  trouble  fre- 
quently met  with  among  sailors  who  have  subsisted  too 
largely  upon  salty  foods.  Nevertheless  such  foods  are 
very  useful,  and  if  a  quantity  of  fresh  food  is  used  with 
them  they  may  be  used  very  advantageously  as  part  of 
our  diet.  In  preparing  such  foods  for  the  table  they 
should  be  soaked  in  water  to  remove  as  much  of  the  salt 
as  possible. 

Vinegar.  Acetic  acid  is  another  material  used  legiti- 
mately for  the  preservation  of  certain  kinds  of  food  prod- 
ucts. In  its  best  known  form,  vinegar,  it  is  the  basis 
of  the  preservation  of  all  kinds  of  pickles.  The  acetic 
acid  in  these  cases  serves  two  purposes  :  (i)  It  gives  a  new 
flavor  to  the  material,  rendering  it  very  sour.  (2)  It  pro- 
tects the  product  almost  totally  from  the  action  of  bacteria. 
The  pickling  of  cucumbers  has  become  a  great  industry, 
green  cucumbers  being  more  extensively  used  for  the  pur- 
pose than  any  other  material.  The  vinegar  is  frequently 
mixed  with  spices,  both  for  the  purpose  of  added  flavor 
and  to  aid  in  the  preservation.  Although  pickled  vegetables 
keep  well,  they  do  not  keep  indefinitely.  Pickle  brine 
sometimes  becomes  covered  with  a  scum  composed  of  bac- 
teria, and  the  pickles  themselves  may  grow  soft  from  decay. 
If  the  pickles  are  taken  out  and  boiled  for  a  few  minutes, 


166  BACTERIA,  YEASTS,  AND    MOLDS 

the  microorganisms  will  be  destroyed,  the  trouble  may 
be  checked  and  the  pickles  preserved.  It  is  practically 
important  to  know  that  pickles  should  not  be  kept  in 
glazed  ware,  since  the  acetic  acid  may  unite  with  the 
glazing  and  make  unwholesome  products.  Glassware 
receptacles  are  best  for  the  holding  of  pickles. 

In  a  somewhat  modified  way  acetic  acid  or  lactic  acid 
is  the  basis  of  certain  other  preserved  foods.  Saner- 
kraut,  for  example,  is  cabbage  protected  from  putre- 
factive fermentation  by  allowing  it  to  sour  and  develop 
acids.  Among  these,  acetic  acid  is  somewhat  prominent, 
but  lactic  acid  is  also  found.  The  acid  in  this  case  is 
formed  in  the  cabbage  by  the  growth  of  acid-producing 
bacteria,  and  after  it  is  formed  it  prevents  the  growth 
of  other  putrefactive  bacteria,  thus  making  it  possible 
to  preserve  for  a  long  time  the  vegetable  material  which 
would  otherwise  undergo  putrefaction.  Here  we  actually 
have  an  instance  of  one  kind  of  harmless  microorgan- 
ism protecting  food  from  the  action  of  other  species.  A 
similar  food  product  is  sometimes  made  from  beans  which 
are  allowed  to  sour  and  are  thus  preserved  from  further 
decay. 

Any  substance  can  be  preserved  from  bacterial  action 
if  it  can  be  soaked  in  vinegar  or  other  acid,  and  it  is 
therefore  possible  in  the  household  to  convert  into  either 
sour  or  sweet  pickles  a  considerable  variety  of  vegetables. 
The  use  of  vinegar  for  this  purpose  is  very  limited, 
mostly  confined  to  green  fruits  and  vegetables,  although 
fish  or  flesh  is  occasionally  treated  in  the  same  way.  The 
product  obtained  is  used  as  a  flavor  to  our  diet  rather  than 
as  a  food. 


SPICES   AS   PRESERVATIVES  167 

Spices.  Many  of  the  spices  common  in  the  household 
are  more  or  less  efficient  as  antiseptics,  and  when  added 
to  food  material  will  preserve  it  from  putrefaction.  Their 
use  is  quite  general  in  certain  household  products.  For 
example,  mince-meat  is  a  watery  mixture  which  under 
ordinary  circumstances  would  readily  putrefy.  Both  the 
meat  and  the  apple  in  it  would  by  themselves  undergo 
putrefaction  and  decay ;  but  when  they  are  made  into 
mince-meat,  and  spices,  boiled  cider,  and  some  other  mate- 
rials added,  the  entire  mixture  forms  a  mass  which,  though 
not  absolutely  protected  from  the  growth  of  microorgan- 
isms, is  ordinarily  incapable  of  supporting  the  growth  of 
the  putrefactive  and  decaying  bacteria  which  would  natu- 
rally appear  in  the  ingredients.  The  antiseptic  effect  is 
produced  chiefly  by  the  spices,  and  if  the  housewife  should 
leave  these  out  she  would  have  a  putrefying  mass  in  a  short 
time.  Such  material  is  not,  however,  completely  protected 
from  mold  growth.  It  will  keep  longer  if  the  apple  is  left 
to  be  added  at  the  time  of  using,  and,  of  course,  it  will  keep 
best  in  a  cool  temperature.  In  a  warm  temperature  the 
effect  of  the  spices  is  not  sufficient  to  prevent  a  more  or 
less  troublesome  fermentation  and  decay,  and  particularly 
molding. 

In  ordinary  sausages  and  salads  the  same  principle  is 
concerned.  Sausage  meat  is  made  of  material  which  is 
subject  to  rapid  putrefaction,  but  in  cool  weather  it  may 
be  preserved  for  a  long  time.  Here  we  have  again  an 
example  of  a  readily  putrescible  material  prevented  from 
decay  by  the  presence  of  the  slightly  antiseptic  spices, 
like  salt,  sage,  etc.  The  spices  in  the  sausages  have 
really  a  twofold  purpose.  Not  only  do  they  protect  the 


168  BACTERIA,   YEASTS,  AND    MOLDS 

materials  for  a  time  from  putrefaction,  but  they  give  to 
them  the  peculiar  flavor  which  is  desired.  In  the  case  of 
sausages,  as  in  mince-meat,  the  spices  are  not  sufficient 
to  prevent  putrefaction  absolutely,  and  consequently  in 
the  warm  summer  weather  it  is  not  very  easy  to  preserve 
them.  Sausages,  like  mince-meat,  are  generally  made  in 
cold  weather,  for  under  such  circumstances  they  may  be 
preserved  without  trouble  for  a  considerable  length  of 
time. 

In  a  somewhat  similar  way,  as  we  have  already  noticed, 
hops  are  used  for  aiding  in  the  preservation  of  a  yeast 
brew.  They  are  also  frequently  used  in  making  beer,  to 
which  they  not  only  impart  a  desired  flavor  but  also  aid 
in  preventing  the  decay  of  materials  present  which  would 
readily  support  the  growth  of  bacteria.  Fruit  cake  of 
certain  grades  is  preserved  from  spoiling  chiefly  by  the 
spices  it  contains.  Nearly  all  strong  spices  have  an  anti- 
septic power  when  mixed  with  foods,  and  protect  them  to 
a  greater  or  less  extent  from  bacterial  action.  This  fact 
is  made  use  of  quite  extensively  by  different  nations  ; 
for  most  countries  have  special  spiced  foods  preserved  in 
this  way,  many  of  which  are  not  known  to  people  outside 
of  the  localities  where  they  are  made.  Spices  are  thus  of 
much  value  both  as  a  means  of  imparting  flavor  and  as 
a  preservative,  but  they  never  preserve  the  original  taste 
of  the  foods.  Many  spiced  foods  are  used  simply  as 
condiments  rather  than  as  nourishment. 


CHAPTER    XII 
PRESERVATION    BY    CANNING 

The  addition  of  mild  preservatives  like  sugar,  salt, 
spices,  vinegar,  etc.,  while  it  makes  possible  the  preser- 
vation of  many  kinds  of  food,  very  decidedly  changes 
their  nature.  The  flavor  is  totally  changed,  and  in  some 
cases  the  food  is  rendered  less  digestible ;  hence  its  food 
value  is  lowered.  These  methods  of  preserving  food  are 
very  useful  for  some  purposes,  but  they  cannot  be  used 
for  all  kinds  of  food.  In  many  cases  the  change  of  flavor 
would  be  so  decided  and  the  change  in  the  nature  of  the 
food  so  great  as  largely  to  destroy  the  material  for  subse- 
quent purposes.  None  of  the  methods  preserve  the  food 
in  anything  like  its  natural  condition. 

WHAT  is   CANNING  ? 

A  method  of  preservation  based  upon  the  simple  plan 
of  keeping  bacteria  away  from  food  products  has  been 
devised  in  the  last  century.  This  has  come  more  and  more 
into  common  use,  until  to-day  it  is  employed  to  an  almost 
incredible  extent.  The  method  is  spoken  of  as  canning. 
The  food  is  not  treated  by  any  antiseptic  for  the  pre- 
vention of  bacterial  growth,  but  reliance  is  placed  simply 
upon  devices  for  keeping  all  bacteria  from  it.  If  this  can 
be  done,  the  food  will  not  be  subject  to  their  action,  and 
will  never  spoil. 

169 


I/O  BACTERIA,  YEASTS,  AND    MOLDS 

We  have  already  noticed  that  bacteria  are  almost  uni- 
versally distributed  in  earth,  air,  and  water.  This  fact 
makes  it  extremely  difficult  to  protect  food  from  their 
action,  and,  indeed,  without  special  devices  it  is  quite 
impossible  to  do  so.  All  food  material — meats,  fruits,  or 
vegetables  —  is  sure  to  contain  bacteria  when  it  reaches 
the  home  or  the  canning  factory.  From  some  source, 
either  air,  water,  or  earth,  every  kind  of  food  material  is 
sure  to  become  contaminated.  Every  one  must  recognize, 
then,  that  bacteria  will  be  found  with  absolute  certainty  in 
every  kind  of  fresh  food. 

Hence  the  process  of  keeping  food  by  protecting  it  from 
bacteria  must  consist  of  two  steps :  (i)  Some  means  must 
be  devised  for  removing  the  bacteria  already  present  in 
the  food.  (2)  The  access  of  all  other  bacteria  must  be 
absolutely  prevented.  If  these  two  objects  can  be  accom- 
plished, the  food  will  be  protected  from  bacterial  action 
and,  thus  protected,  may  be  preserved  indefinitely.  Food 
thus  guarded  may  be  kept  for  any  number  of  months.  No 
limit  has  ever  been  found,  and  we  have  no  reason  for  ques- 
tioning that  it  might  be  preserved  for  centuries  without 
any  subsequent  change,  provided  it  could  be  kept  abso- 
lutely free  from  the  attack  of  microorganisms.  This 
method,  therefore,  offers  almost  unlimited  possibilities  in 
the  way  of  preserving  food  for  future  use.  It  demands 
care  in  its  application,  but  the  results,  when  properly 
obtained,  are  permanent. 

i.  Destroying  the  Bacteria  Present.  The  removal  from 
any  food  material  of  bacteria  already  present  is  generally 
brought  about  by  the  action  of  high  heat.  We  have 
already  noticed  that  a  sufficiently  high  heat  is  fatal  to  all 


STERILIZATION    FOR   CANNING  171 

forms  of  life,  and  hence  the  simple  heating  of  food  will 
destroy  all  bacteria.  The  material  to  be  canned  must  be 
cut  up  into  pieces  of  convenient  size,  which  will  depend 
somewhat  upon  the  kind  of  material.  In  general,  the 
larger  the  pieces,  the  more  attractive  the  appearance  of 
the  product  when  finished  but  the  greater  the  difficulty 
of  canning.  Cherries,  plums,  and  berries  can  be  left 
whole.  Pears  are  cut  into  halves  or  quarters,  while  apples 
are  commonly  cut  into  smaller  pieces.  These  pieces  are 
to  be  placed  in  water  and  the  whole  brought  to  a  brisk 
boil, — this  temperature  being  chosen  because  it  is  easily 
obtained  and  because  it  is  sufficient  in  most  cases  to  destroy 
the  bacterial  life.  The  process  of  canning  is,  therefore, 
applicable  only  to  materials  that  are  not  greatly  injured  by 
immersion  in  water  and  subsequent  boiling.  Hence  it  is 
useful  for  foods  which  cannot  be  well  preserved  by  drying. 
In  the  application  of  heat  several  points  must  be  borne 
in  mind.  I.  It  must  be  remembered  that  the  destruc- 
tion of  the  bacteria  must  be  absolute.  If  a  single  indi- 
vidual bacterium  is  left  alive  in  the  food  after  the  boiling, 
the  whole  process  is  useless,  and  the  canning  will  be  a 
total  failure.  One  live  bacterium  will  be  capable  of  grow- 
ing and  multiplying,  producing  a  subsequent  putrefaction 
and  destruction  of  food  with  just  as  great  certainty,  though 
not  so  quickly,  as  if  a  million  of  them  were  left  alive.  The 
preliminary  heating  must  therefore  be  a  complete  sterili- 
zation, that  is,  a  heating  so  thorough  that  every  individual 
bacterium  is  destroyed.  No  half-way  processes  are  of  any 
use  whatsoever;  it  must  be  total  and  absolute.  This  is 
by  no  means  easy,  and  most  failures  in  canning  are  due 
to  the  inability  to  bring  about  this  complete  destruction. 


BACTERIA,  YEASTS,  AND  MOLDS 

If  a  housewife  finds  that  a  portion  of  her  canned  preserves 
is  spoiled,  she  may  be  sure  that  the  original  heating  was 
insufficient. 

2.  It  must  be  remembered  that  the  amount  of  heat 
required  to  destroy  different  species  of  bacteria  is  not 
always  the  same.  While  most  actively  growing  bacteria 
are  destroyed  by  a  moderate  heat,  and  quickly  killed  by 
boiling,  certain  bacteria  spores,  as  already  noticed,  are 
capable  of  standing  much  greater  heat.  Some  kinds  of 
bacteria  produce  spores  that  may  be  boiled  for  a  few 
moments,  or,  indeed,  for  an  hour,  without  being  wholly 
destroyed.  From  this  it  follows  that  a  short  boiling 
is  not  always  sufficient  to  destroy  bacterial  life.  If  the 
food  material  chances  to  contain  some  of  these  resisting 
spores,  the  brief  boiling  commonly  adopted  in  the  pro- 
cess of  canning  will  not  kill  them,  and  it  will  inevitably 
happen  that  the  food,  if  canned,  will  undergo  putrefac- 
tion because  of  the  growth  of  the  spores  that  were  left 
uninjured.  If  on  the  other  hand  the  food  in  question 
does  not  chance  to  contain  such  spores,  a  few  moments' 
boiling  is  quite  sufficient  to  protect  the  material  perfectly 
from  later  decay. 

It  is  a  well-known  fact  that  the  process  of  canning  is 
not  equally  successful  with  all  kinds  of  foods.  Some  sub- 
stances (rhubarb}  contain  a  material  that  acts  as  a  par- 
tial antiseptic  and  can  be  preserved  very  easily.  Others, 
like  most  fruits,  require  a  little  more  care,  but  are  easily 
preserved ;  while  others,  in  spite  of  the  ordinary  precau- 
tions, will  frequently  show  subsequent  signs  of  decay. 
The  canning  of  tomatoes  has  always  given  trouble  to  the 
housewife.  In  former  years  it  was  thought  to  be  an 


DIFFICULTIES   OF   CANNING  173 

impossibility  to  can  green  corn,  and  the  preservation  of  peas 
and  beans  has  proved  to  be  even  more  difficult.  While 
all  of  these  products  are  successfully  preserved  by  canning 
to-day,  it  is  chiefly  done  in  factories  ;  for  they  are  far  more 
difficult  to  preserve  in  this  way  than  a  large  number  of 
other  foods  which  are  more  commonly  preserved  in  the 
home.  The  problem  of  canning  any  product,  whether  it 
be  fruit,  tomatoes,  corn,  or  peas,  is  simply  that  of  totally 
destroying  the  bacteria  that  may  be 
present.  If  the  material  chances  to 
contain  only  the  bacteria  that  are 
unable  to  produce  spores,  as  with 
most  fruits,  it  is  quite  easy  to 
destroy  them  by  simple  boiling. 
Green  corn,  however,  has  been  *V 
found  by  microscopic  study  to  con-  FIG.  63.  Spore-producing 
tain  a  considerable  number  of  a  cer-  bacteria  found  in  canned 
tain  kind  of  bacteria  which  develop 

spores  capable  of  resisting  very  high  heat  (Fig.  63).  These 
bacteria  have  been  found  on  the  corn  husks  while  grow- 
ing in  the  field,  on  the  corn  cobs,  and  also  in  the  green 
corn.  They  are  difficult  to  destroy  by  heat,  and  hence 
the  successful  canning  of  corn  has  been  regarded  in 
past  years  as  an  impossibility.  The  presence  of  two  or 
three  or  even  one  of  these  highly  resisting  spores  may 
be  quite  sufficient  to  make  the  ordinary  method  of  can- 
ning quite  ineffectual.  Although  little  microscopic  study 
has  been  directed  to  other  similar  problems,  like  the  can- 
ning of  tomatoes  and  peas,  there  is  no  doubt  that  the 
trouble  is  due  to  the  presence  of  spore-bearing  bacteria 
which  resist  the  temperature  of  ordinary  boiling. 


1/4      BACTERIA,  YEASTS,  AND  MOLDS 

The  remedy  in  all  such  cases  is  greater  heat,  since  no 
satisfactory  means  of  destroying  bacteria  is  known  except 
the  application  of  heat.  Even  spores  may  be  perfectly 
destroyed  if  the  proper  method  is  adopted. 

Higher  Heat.  Common  liquids,  when  boiled  in  open 
vessels,  cannot  be  heated  above  212°,  no  matter  how  brisk 
the  boiling  ;  but  if  boiled  in  closed  vessels  under  pressure 
the  temperature  may  be  raised  much  higher.  A  tempera- 
ture of  212°  does  not  destroy  spores,  but  a  few  degrees 
higher  will  do  so.  If  the  material  is  boiled  under  pressure 
of  a  few  pounds  only,  such  a  temperature  is  easily  obtained, 
and  if  it  is  maintained  for  a  short  time  the  spores  will  be 
destroyed.  In  the  household  it  is  rarely  possible  to  use 
apparatus  for  this  purpose;  but  in  canning  factories  there 
is  no  difficulty  in  constructing  and  using  devices  for  heat- 
ing under  pressure.  This  method  of  heating  is  commonly 
adopted  for  the  sterilization  of  food  products  which  are 
difficult  to  can  because  of  the  presence  of  spores. 

Longer  Heating.  Higher  temperatures  are  not  easily 
obtained  in  the  household,  but  the  spores  may  be  killed 
by  simply  prolonging  the  boiling.  If  spore-bearing  mate- 
rial is  boiled  for  a  sufficient  time,  the  spores  are  eventually 
totally  destroyed.  The  length  of  time  necessary  for  the 
purpose  cannot  be  stated  exactly,  for  it  will  depend  very 
largely  upon  the  vigor  of  the  boiling  and  the  nature  of  the 
food.  For  the  thorough  sterilization  of  peas  an  hour,  or 
even  two  hours,  may  be  needed,  and  an  equal  time  is 
required  for  corn  or  beans.  Tomatoes  do  not  require 
quite  so  much  time.  Any  material  will  be  more  surely 
sterilized  if  placed  at  first  in  cold  water  and  then  brought 
to  a  boil,  than  if  placed  immediately  in  boiling  water. 


HERMETICAL  SEALING  175 

Nearly  all  failures  in  canning  are  due  to  an  insufficient 
amount  of  heating  at  the  outset.  In  the  canning  of 
fruits,  which  is  the  kind  of  preserving  most  commonly 
performed  at  home,  there  is  seldom  any  special  difficulty, 
since  fruits  do  not  as  a  rule  contain  resisting  spores. 
In  the  majority  of  cases,  therefore,  a  vigorous  boiling  of 
fruits  for  a  few  moments  is  sufficient  to  destroy  bacterial 
life,  after  which  the  materials  can  be  canned  with  perfect 
success.  It  must  be  remembered,  however,  that  absolute 
certainty  cannot  be  reached  by  simple  boiling,  and  that 
the  employing  of  this  method  will  result  in  occasional 
failures.  Once  in  a  while  a  can  will  become  decayed, 
though  the  rest  of  the  same  lot  will  be  preserved  in  the 
proper  fashion.  The  difference  in  these  cases  is  doubt- 
less due  to  the  accidental  presence  of  some  spore-producing 
bacterium  which  happened  to  get  into  one  of  the  cans  and 
not  into  the  others. 

2.  Preservation.  ,  After  the  food  has  once  been  de- 
prived of  bacteria  (sterilized),  it  must  be  protected  from 
the  subsequent  access  of  all  kinds  of  microorganisms. 
Since  bacteria  are  always  present  in  the  air,  any  of 
these  sterilized  products  will  surely  be  reinoculated  if 
exposed,  and  the  new  bacteria  would  soon  spoil  the  food. 
The  practical  method  of  keeping  bacteria  out  is,  there- 
fore, that  of  sealing  the  contents  hermetically.  In  the 
laboratory  it  is  possible  to  preserve  foods  without  sealing 
by  simply  filtering  all  the  air  that  reaches  them  through 
something  fine  enough  to  'exclude  bacteria.  Bacteriolo- 
gists have  found  that  the  air  which  passes  through  cotton 
is  deprived  of  all  bacteria.  If,  therefore,  any  sterilized 
material  is  placed  in  bottles,  tubes,  or  vials  which  are 


BACTERIA,  YEASTS,  AND  MOLDS 


tightly  plugged  with  cotton,  as  shown  in  Fig.  64,  it  will 
be  perfectly  protected  from  the  invasion  of  bacteria.  A 
knowledge  of  this  fact  may  be  of  some  practi- 
cal importance,  even  in  the  household,  in  case 
it  is  desired  to  preserve  something  for  a  short 
time  only  and  one  does  not  want  to  go  to  the 
trouble  of  hermetical  sealing.  But  such  a 
method  is  quite  impracticable  for  the  ordi- 
nary canning  of  food.  At  best  it  is  of  only 
temporary  utility,  for,  though  cotton  keeps 
all  bacteria  away  from  the  sterilized  material, 
it  will  not  wholly  exclude  molds,  and  there- 
fore cannot  preserve  indefinitely. 

Hermetical  sealing,  which  will  prevent  all 
subsequent  access  of  air,  is  extremely  easy  to 
accomplish  and  is  thoroughly  effective.  The 
material  must  be  sealed  in  some  proper  re- 
ceptacle while  still  hot  from  the  boiling,  for 
it  is  at  this  time  sterile,  and  if  sealed  at  once 
has  no  opportunity  of  becoming  inoculated 
with  more  bacteria. 

The  devices  for  hermetical  sealing  are 
served  cher-  numerous.  In  earlier  days  the  housewife 
ries,  showing  employed  ordinary  bottles,  which  were  filled 

that   the   ex- 
clusion of  air  with  the  material,  then  plugged  tightly  with 

is  not  neces-  corks,  and  sealed  with  rosin  or  something  of 
saryforpres-  the  sort  to  exciucie  an  air      The  invention 

ervation. 

of  the  modern  fruit  jar  with  its  rubber  ring 
and  convenient  top  has  done  away  with  all  such  crude 
devices.  The  fruit  jar  with  its  variously  devised  top  is 
a  perfectly  effectual  means  for  excluding  air  and  hence 


FIG.  64.      Pre- 


THE   FRUIT  JAR  177 

for  keeping  out  all  microorganisms  (Fig.  65).  The  sig- 
nificant feature  of  these  fruit  jars  is  the  rubber  ring  a, 
which  is  clamped  tightly  upon  a  flat  ledge  on  the  jar  c,  by 
means  of  the  cover  b,  so  made  that  heavy  pressure  can  be 
exerted  upon  the  rubber.  This  pressure  upon  the  rub- 
ber effectually  excludes  all  air  and  all  bacteria.  Fresh 
rubber  rings  should  be  used  each  time  the  jar  is  filled, 
since  the  efficiency  of  the  sealing  depends  upon  the  soft- 
ness and  elasticity  of  ^— —  ====. 
the  rubber;  if  this 
gets  hard,  as  it  will 
in  a  few  months,  the 
sealing  will  not  be 
effectual.  Of  course 
the  whole  jar  must 

be   Sterilized    before    FIG.  65.     The   top  of   a  common  fruit   jar. 

being  filled.     To  do      At  a  is  the  rubber  rins  uPon  which  the  suc' 

cess  of  the  sealing  is  dependent. 

this  it  is  best  to  place 

it  in  cold  water,  bringing  the  water  to  a  vigorous  boil,  and 

then  fill  the  jar  while  it  is  still  hot. 

The  glass  fruit  jar  is  almost  universally  used  in  the 
home,  is  very  convenient,  and  can  be  used  again  and 
again.  But  in  canning  factories  the  use  of  tin  cans  is 
largely  adopted,  since  they  are  less  expensive  and  are 
to  be  used  but  once.  The  principle  of  their  use,  how- 
ever, is  exactly  the  same  as  that  of  the  glass  jar,  although 
the  details  are  different.  The  material  to  be  canned, 
with  or  without  previous  boiling,  is  put  in  the  tin  can, 
upon  which  a  cover  is  placed  and  sealed  firmly  by  sol- 
dering, the  whole  now  being  closed  to  the  air  except 
for  a  small  opening  in  the  cover.  Then  the  can,  with 


1/8  BACTERIA,  YEASTS,  AND    MOLDS 

its  contents,  is  placed  in  a  convenient  heating  appa- 
ratus for  thorough  sterilization,  the  opening  in  the  top 
being  sufficient  for  the  exit  of  steam  and  for  preventing 
internal  pressure,  which  might  give  rise  to  an  explosion. 
In  some  factories  it  is  sometimes  customary  to  heat  the 
product  in  a  bath  of  CaCl,  which  makes  it  possible  to 
obtain  a  temperature  of  260°-  — quite  sufficient  to  sterilize 
the  contents  of  the  can,  even  though  it  contain  resisting 
spores,  as  will  be  the  case  with  peas  or  corn.  While  the 
material  is  still  hot  a  drop  of  solder  is  placed  upon  the 
opening  in  the  top  of  the  can.  This  thoroughly  seals  it 
and  the  work  is  done.  It  is  customary  to  keep  the  cans 
in  the  factory  for  a  while  in  order  to  test  the  efficacy 
of  the  work.  Any  cans  which  later  are  found  to  be 
swollen,  indicating  the  accumulation  of  gas  on  the  inside, 
are  discarded  as  ruined.  In  the  ordinary  process  it  fre- 
quently happens  that  an  occasional  can  either  fails  of  ster- 
ilization or  of  complete  sealing;  the  result  of  which  is  a 
subsequent  ruin  of  the  product.  Canning  factories  some- 
times suffer  great  loss  from  the  spoiling  of  their  products. 
In  all  these  cases  the  cause  is  probably  the  presence 
of  resisting  spores,  and  the  remedy  is  the  application  of 
greater  heat.  A  knowledge  of  this  fact  has  enabled  can- 
ning establishments  in  recent  years  to  avoid  in  great 
measure  their  previous  losses. 

In  certain  kinds  of  canned  food  it  has  been  customary  to  add 
some  mild  antiseptic  to  aid  in  the  subsequent  preserva- 
tion. The  material  most  commonly  used  for  this  purpose 
is  borax,  which  is  frequently  found  in  cans  of  meat.  Its 
purpose  is  to  check  the  development  of  any  bacteria  that 
may  be  left  in  the  meat  after  the  process  of  canning. 


PRESERVATIVES   USED   IN  CANNING  179 

From  the  facts  already  given  it  will  be  seen  that  the 
presence  of  borax  in  canned  foods  is  totally  unnecessary, 
provided  sufficient  care  is  taken  in  the  canning.  Its 
use  was  a  means  of  covering  up  a  lack  of  thoroughness 
in  canning,  and  it  has  been  found  in  the  cheaper  products. 
If  the  material  had  not  been  heated  enough  to  produce 
complete  sterilization,  it  might  still  be  preserved  in  cans 
if  sufficient  borax  were  added.  In  large  packing  factories 
where  a  great  amount  of  food,  particularly  meat,  is  to 
be  canned  at  once,  it  had  become  quite  common  to  use 
a  certain  amount  of  such  a  preservative  to  cover  up  this 
lack  of  complete  sterilization  and  prevent  subsequent  loss. 
The  method  is  of  course  more  economical,  because  it  does 
not  require  so  much  heat  and  because  there  is  a  very 
much  smaller  per  cent  of  loss.  Whether  the  material  thus 
preserved  is  unwholesome  is  a  question  that  has  not  yet  been 
positively  settled,  but  the  sale  of  it  is  to-day  forbidden  by 
the  national  Pure  Food  Law.  In  fruit  canning  in  the 
household  it  may  be  given  as  a  universal  rule  that  no  dis- 
infectants of  any  sort  should  be  used.  If  the  housewife 
cannot  satisfactorily  preserve  her  fruits  without  them,  she 
would  do  very  much  better  to  depend  upon  the  commercial 
products  which  she  can  buy  at  the  store.  At  all  events,  no 
one  should  under  any  circumstances  resort  to  the  use  of 
borax,  preservaline,  antifermentine,  or  any  of  the  other 
materials  put  upon  the  market  for  preventing  fermentation. 
They  are  dangerous  to  use,  they  are  at  least  partly  poisonous, 
and  their  use  in  any  form  should  be  absolutely  avoided  in 
domestic  work. 

Practically  any  type  of   food   can   be   preserved  by   can- 
ning.    Some    materials,     however,    are    very    much    more 


180  BACTERIA,  YEASTS,  AND   MOLDS 

easily  preserved  than  others.  Meats  are  preserved  with 
great  ease,  but  it  is  rarely  worth  while  in  the  household 
to  can  meat,  since  fresh  meat  can  be  bought  in  civilized 
countries  at  all  seasons  of  the  year.  When  one  wants 
canned  meats  it  is  better  to  depend  upon  the  product 
bought  in  the  market  than  to  go  to  the  trouble  of  canning. 
The  same  may  be  said  of  tomatoes,  corn,  peas,  or  beans.  All 
of  these  materials  may  be  canned  successfully  in  an  ordi- 
nary household,  but  it  requires  long  heating  and  special 
care,  and  at  best  there  will  be  many  failures.  Consequently 
such  materials,  when  canned  in  the  home,  may  be  very 
expensive  because  of  the  considerable  amount  that  must 
be  thrown  away.  In  the  canning  factory,  however,  because 
of  greater  experience  and  better  facilities,  these  foods 
can  be  preserved  much  more  successfully  and  cheaply. 
Moreover  the  commercial  products  in  these  cases  are  of  a 
very  satisfactory  quality  and  very  cheap.  If  for  any  reason 
a  housewife  has  on  hand  a  large  quantity  of  tomatoes 
which  must  be  canned  or  thrown  away,  it  may  be  econom- 
ical to  can  them  at  home,  always  remembering  that  they 
require  more  heat  and  more  care  than  most  other  fruits. 
But  except  under  such  conditions  it  is  better  and  cheaper 
to  depend  upon  the  market  for  canned  tomatoes,  peas,  and 
corn.  The  market  products  are  more  reliable,  consider- 
ably cheaper,  and  usually  nearly  or  quite  as  good  as  those 
obtained  by  home  canning. 

Concerning  other  materials,  however,  it  is  economical 
and  frequently  advantageous  to  adopt  the  process  of  can- 
ning in  the  household.  Most  forms  of  fruit — apples, 
pears,  cherries,  peaches,  grapes,  berries,  etc.  —  are  canned 
without  much  difficulty,  requiring  only  a  moderate  boiling 


VALUE    OF   CANNED   GOODS  l8l 

and  a  careful  sealing  in  fruit  jars.  The  material  thus 
prepared  is  usually  of  a  better  flavor,  because  more  care- 
fully prepared,  and  more  satisfactory  than  much  that  can 
be  bought  in  the  markets,  in  the  preparation  of  which 
wholesale  methods  have  been  necessary.  For  the  house- 
hold, therefore,  canning  is  chiefly  applicable  to  fruits,  and 
it  furnishes  a  means  of  keeping  for  winter  use  many 
delightful  delicacies. 

The  process  of  canning  has  wrought  a  wonderful  change 
in  civilization.  It  has  made  possible  the  use  of  great 
quantities  of  material  which  previously  were  sure  to  decay 
before  they  could  be  used.  It  is  possible  to  take  any  crop 
which  is  produced  in  abundance  during  a  short  season  and 
preserve  it  indefinitely  for  future  use.  It  has  brought 
about  a  great  expansion  of  the  food  possibilities  of  the 
human  race  and  -a  very  great  change  in  the  habits  of 
civilization. 

Canned  food  is,  however,  always  changed  in  character 
by  cooking,  although  materials  which  are  ordinarily  cooked 
before  they  are  eaten  may,  of  course,  be  canned  without 
further  change.  The  most  noticeable  effect  of  the  process 
is  the  total  disappearance  of  the  original  flavors.  Canned 
fruit  has  a  flavor  of  its  own  and  oftentimes  a  very  pleas- 
ant one,  but  the  flavor  of  the  fresh  fruit  is  usually  more 
agreeable.  Experience  has  shown  that  a  diet  of  canned 
foods  alone  is  not  wholly  satisfactory,  although  arctic 
explorers  have  learned  that  they  can  live  upon  them  much 
more  healthfully  than  they  can  upon  salt  foods,  which 
were  the  staple  diet  on  shipboard  before  the  extended 
adoption  of  canning.  Canned  foods  are  valuable,  but 
they  should  not  be  used  exclusively. 


CHAPTER    XIII 

MILK;   EGGS;    PTOMAINE    POISONING 
BACTERIA  IN  MILK 

It  is  more  difficult  to  preserve  a  supply  of  good  milk 
than  of  almost  any  other  food  product.  This  is  due  to 
three  reasons  :  (i)  The  number  of  bacteria,  under  ordinary 
circumstances,  is  greater  than  in  any  other  food  product. 
(2)  Milk  furnishes  an  exceptionally  favorable  food  for 
bacteria.  (3)  The  changes  which  these  bacteria  produce  in 
milk  are  very  decided  and  take  place  with  great  rapidity. 
These  three  factors  together  make  it  difficult  to  preserve 
milk  in  the  household  without  exceptional  precautions. 

The  bacteria  present  in  milk  are  not  only  numerous, 
but  they  comprise  many  kinds  (Fig.  66).  Milk  as  it  is 
secreted  by  the  healthy  cow  does  not  contain  bacteria,  but 
it  has  a  chance  of  contamination  with  microorganisms 
from  a  variety  of  sources,  and  even  a  few  moments  after 
the  milk  has  been  drawn  it  contains  organisms  in  large 
numbers.  The  chief  sources  of  these  organisms  are : 
(i)  the  bacteria  in  the  milk  ducts  which  are  washed  into 
the  milk  can  during  the  milking  ;  (2)  the  dust  that  is  likely 
to  be  floating  in  the  air  of  the  barn  or  milking  stall  where 
the  milk  is  drawn ;  (3)  the  milk  vessels,  which  are  rarely 
washed  perfectly  clean  ;  (4)  the  dirt  and  filth  that  are 
always  clinging  to  the  hairs  of  the  cow  and  which  fall  into 

182 


PTOMAINE    POISONING 


183 


the  milk  pail  during  the  milking  ;  (5)  bacteria  from  the 
hands  and  clothing  of  the  milker. 

The  number  of  bacteria  found  even  in  fresh  milk  is 
extremely  great,  particularly  if  the  milk  be  drawn  without 
special  precautions  for  cleanliness.  Thousands  and  even 
hundreds  of  thousands  are  sometimes  found  in  each  cubic 
inch.  These 
bacteria  grow 
rapidly,  inasmuch 
as  milk  is  warm 
when  drawn 
from  the  cow, 
and  by  the  time  it 
reaches  the  con- 
sumer in  the  city 
the  milk  is  likely 
to  contain  these 
microorganisms 
in  in  cred  ible 
numbers.  The 

exact  numbers,  FIG.  66.  Milk  as  shown  under  the  microscope,  show- 
however,  are  mat-  ing  numerous  bacteria,  a,  common  lactic  bacteria ; 
ters  of  no  Special  b>  common  cocci ;  c,  fat  globules ;  d,  cells. 

importance  to  us,  for  fortunately  most  of  the  bacteria  in 
milk  are  harmless.  Some  of  them,  indeed,  are  useful,  and, 
while  occasionally  troublesome  bacteria  get  into  milk,  as  a 
rule  we  may  look  upon  the  milk  bacteria  as  doing  no  injury 
to  the  health  of  the  person  drinking  it  (Fig.  67). 

Effect  of  Bacteria  upon  the  Milk.  But  the  housewife 
is  interested  in  the  effect  of  the  growth  of  bacteria  upon 
the  milk  itself.  The  bacteria  which  grow  most  rapidly  in 


1 84 


BACTERIA,  YEASTS,  AND  MOLDS 


milk  belong  to  a  type  known  as  lactic  bacteria  (Fig.  67). 
These  produce  a  change  in  the  milk  sugar,  converting  it 
into  lactic  acid,  which  causes  the  milk  to  taste  sour  and 
curdle.  Curdling  and  souring  will  never  occur  if  bacteria 
can  be  kept  out  of  the  milk.  Although  the  souring  is  a 
oo  n  nuisance,  it  does  not  injure 

>g«  9qrf>_  the  wholesomeness  of  the 
milk,  and  sour  milk  could 
be  used  freely  were  it  not 
for  its  unpleasant  taste. 
Indeed,  souring  is,  under 
some  circumstances,  desir- 
able, since  milk  properly 
soured  is  protected  from  a 
variety  of  other  changes 
far  less  agreeable.  If  the 
lactic  bacteria  do  not  cause 
the  milk  to  sour,  it  is 
almost  sure  to  putrefy,  and 

i ,  the  most  common  lactic  bacterium,  B.  lactis  putrefaction  is  far  more 

acidi;    2,  a  less  common   lactic  bacterium  unpleasant     and      Unwhole- 
n.  lactis  aerogenes ;  3,  common  cocci  found 

in    milk;    4,    a  bacillus    producing    cheese  SOmC    than     Ordinary     SOlir- 

flavors ;  s,  a  common  bacillus  with  no  action  .  .-p.,  .  r        .,, 

on  milk,  *.  «*,7«;    6,  a  bacillus  causing  "lg.        The  SOUring  of  milk, 

slimy  milk,  B.  lactis  viscosus  ;  7  and  8,  com-  therefore,  is  SL  natural  phe- 
mon  organisms  with  no  action  on  milk;  9, 

bacillus  causing  swelling  of  cheese;    10,  a  n  O  m  6  n  O  n,    and    OttC    that 

bacillus  causing  milk  to  become  putrid.  should    be     expected    and 

desired  in  milk  after  it  has  become  a  day  or  two  old. 
Milk  which  will  not  sour  is  suspicious,  unless  it  has  been 
kept  at  a  very  low  temperature  for  preservation. 

Sometimes   milk  a  day  or  two  old  becomes   slimy  or 
slippery  to  the  touch,  rather  sweetish  to  the  taste,  and  is 


9  ^   fo 

FIG.  67.     Group  of  milk  bacteria. 


PRESERVATION    OF    MILK  185 

ruined  for  all  practical  purposes.  There  is  no  special  rea- 
son for  believing  that  such  milk  is  unwholesome ;  but 
people  will  not  drink  it  since  it  is  not  normal  milk.  Milk 
occasionally  undergoes  a  sort  of  putrefaction,  becoming 
tainted  in  smell  and  taste.  Sometimes  it  becomes  blue 
or  red,  and  occasionally  other  changes  take  place  in  it. 
Practically  all  of  these  phenomena  are  due  to  different 
species  of  bacteria,  and  they  may  all  be  prevented  if  the 
growth  of  the  microorganisms  can  be  held  in  check. 
None  of  them,  however,  produce  so  much  trouble  in  the 
household  as  souring,  and  although,  from  the  standpoint 
of  health,  some  of  these  other  types  of  bacterial  action 
are  more  serious  than  the  souring,  the  latter  is  the  phe- 
nomenon which  produces  the  greatest  inconvenience. 

PRESERVATION  OF  MILK 

The  preservation  of  milk,  which  commonly  means  pre- 
venting the  milk  from  souring  within  too  short  a  time,  is 
accomplished  only  by  checking  the  growth  of  bacteria. 
In  considering  the  question  of  furnishing  the  household 
with  good,  sweet,  wholesome  milk,  several  factors  are 
involved  which  must  be  considered  separately. 

i.  Source.  Every  housewife  should  be  very  particular 
about  the  source  from  which  she  obtains  her  milk.  This 
is  a  matter  frequently  overlooked,  and  milk  is  obtained 
without  special  consideration  as  to  its  source,  upon  the 
general  assumption  that  all  milk  is  alike  and  that  it  makes 
little  difference  from  whence  it  comes.  This  is  common 
in  the  families  of  the  rich  and  the  poor,  because  the 
former  leave  the  purchase  to  servants,  and  the  latter  are 


186  BACTERIA,   YEASTS,  AND   MOLDS 

likely  to  buy  the  cheapest  quality.  No  article  of  food 
should  be  so  closely  scrutinized,  for,  although  the  legal 
safeguards  which  the  public  milk  inspection  places  around 
our  milk  supplies  insure  a  tolerably  good  chemical  quality, 
there  is  a  great  difference  in  the  product  from  different 
sources.  It  is  an  absolute  rule  that  cheap  milk  is  always 
poor  milky  and  the  cheaper  the  less  its  value.  It  is  not 
economy  to  purchase  poor  milk,  for,  although  there  may 
be  a  saving  in  the  original  purchase,  the  amount  of  food 
bought  is  less  and  the  danger  attending  its  use  is  much 
greater.  Recognizing,  then,  that  its  value  is  in  propor- 
tion to  its  cost,  we  notice  the  kinds  of  milk  that  may  be 
purchased  in  the  modern  city. 

Sanitary  Dairies.  Certified  Milk.  The  most  expensive 
milk  comes  from  special  dairies  where  great  care  is  taken 
to  keep  everything  in  proper  sanitary  condition.  The 
cows  are  kept  in  first-class  health  and  are  under  the  care 
of  a  veterinarian.  Every  precaution  is  taken  to  exclude 
contagious  diseases  from  contact  with  the  dairy,  and  care 
is  taken  to  keep  everything  clean  and  sanitary.  For  all 
this  care  the  dairyman  must  of  course  be  reimbursed  by 
the  consumer,  and  he  is  obliged  to  charge  a  higher  price. 
In  the  vicinity  of  our  larger  cities  many  of  these  dairies 
have  grown  up  in  the  last  few  years  and  are  to-day  furnish- 
ing an  exceptionally  high  grade  of  sanitary  milk,  for  which 
the  charge  is  commonly  from  twelve  to  fifteen  cents  per 
quart.  Such  milk,  though  the  most  expensive,  is  undoubt- 
edly the  best  and  is  far  safer  than  the  ordinary  milk. 

A  modification  of  this  method  is  the  sale  of  what  is 
called  certified  milk.  This  is  milk  that  is  sold  with  the  cer- 
tificate of  a  special  commission,  commonly  composed  of 


TYPES   OF   CITY   MILK  187 

physicians.  This  commission,  by  means  of  chemical  and 
bacteriological  tests  and  sometimes  by  visits  to  the  dairies, 
insures  itself  that  certain  dairies  produce  milk  of  good 
character  and  under  unexceptionable  conditions.  Exam- 
inations and  tests  of  the  milk  are  made  frequently,  and  if 
it  comes  up  to  the  high  standard  which  is  set,  the  com- 
mission gives  the  dairy  its  certificate,  which  is  then  placed 
upon  each  bottle  of  milk  sold.  Such  a  certificate  assures 
the  customer  that  the  milk  is  thoroughly  reliable. 

Milk  from  the  Ordinary  Milkman.  Milk  from  the  com- 
mon milk  supply  is  less  reliable  and  costs  correspondingly 
less.  Sometimes  this  milk  is  of  a  good  character,  perhaps 
of  as  high  a  grade  as  that  from  the  sanitary  dairies.  At 
other  times,  however,  such  milk  is  not  satisfactory,  because 
it  is  produced  under  conditions  of  unimaginable  filth. 
There  is  no  way  for  the  consumer  in  a  large  city  to  deter- 
mine whether  the  milk  from  the  milkman  is  reliable;  and 
if  milk  is  to  be  purchased  from  an  ordinary  milk  supply, 
one  .must  be  content  with  such  legal  regulations  as  the 
state  can  devise  for  protecting  the  quality  of  milk.  If  one 
lives  in  a  small  community  where  the  milk  is  distributed 
by  the  producer  himself,  it  is  quite  possible  to  know  more 
about  its  quality ;  for  a  little  care  in  selecting  the  most 
cleanly  milkman  will  ordinarily  result  in  obtaining  milk 
that  is  thoroughly  satisfactory. 

Grocery  Milk.  The  poorest  kind  of  milk  that  can  be 
purchased  is  that  upon  which  the  poorer  classes  in  cities 
largely  depend.  This  is  obtained  from  groceries,  and  is 
bought  in  small  quantities.  This  method  of  purchasing 
is  a  necessity  with  the  poorer  classes  who  have  no  re- 
frigerators, for  in  warm  weather  it  is  quite  impossible  to 


188  BACTERIA,  YEASTS,  AND   MOLDS 

preserve  milk  in  a  tenement  house  without  the  use  of  ice. 
The  grocer  keeps  the  milk  on  ice,  and  the  customer  buys 
it  in  small  quantities  to  be  consumed  at  once.  This  would 
be  a  proper  arrangement  if  it  were  not  for  the  fact  that 
poorer  kinds  of  milk  find  their  way  into  these  groceries, 
and  are  likely  to  be  kept  until  old,  so  that  as  a  rule  the 
milk  thus  purchased  is  the  poorest  grade  that  reaches  the 
market.  It  is  usually  sold  at  a  small  price,  but  is  of  such 
poor  quality  that  the  poorer  classes  themselves  would  be 
much  wiser  to  purchase  a  better  grade. 

By  the  removal  of  part  of  its  water  the  keeping  property 
of  milk  may  be  increased.  Condensed  milk  is  such  a  prod- 
uct, which,  after  condensation,  is  commonly  preserved  by  the 
addition  of  about  40^)  sugar  or  by  sterilizing.  It  is  a  useful 
product,  but  cannot  exactly  replace  fresh  milk.  A  type 
sometimes  called  concentrated  milk  has  three  quarters  of 
its  water  removed  by  evaporation  at  140°.  This  destroys 
disease  germs  and  brings  the  milk  into  a  condition  in 
which  it  will  keep  for  many  days.  When,  subsequently, 
the  water  is  restored,  the  material  is  indistinguishable  from 
fresh  milk  and  will  be  easily  substituted  for  it. 

But  our  care  should  not  cease  with  the  scrutiny  of  its 
source.  Even  though  originally  of  the  highest  character, 
milk  will  not  keep  in  our  homes  unless  properly  treated. 
The  keeping  of  milk  depends  upon  temperature  and 
cleanliness  in  the  pantry. 

2.  Milk  Vessels.  Special  care  should  be  given  to  the 
vessels  in  which  milk  is  received  and  kept.  A  large  part 
of  the  trouble  which  the  housewife  experiences  in  keeping 
milk  is  due,  not  to  the  milkman,  nor  to  the  character  of 
the  milk  which  she  purchases,  but  to  the  condition  of  the 


PRESERVATION    OF    MILK  189 

vessel  in  which  she  places  it.  A  milk  pitcher  used  day 
after  day  becomes  filled  with  lactic  acid  bacteria,  and  any 
fresh  milk  poured  into  such  a  receptacle  will  be  sure  to 
sour  in  a  very  short  time.  This  fact  a  housewife  fre- 
quently overlooks.  Milk  vessels  should  be  cleaned  with 
the  greatest  of  care  and  should  be  thoroughly  scrubbed 
with  boiling  water  in  which  there  is  considerable  soap. 
The  soap  "cuts"  the  grease  and  cleans  the  dirt  from  the 
milk  vessels,  and  the  boiling  water  kills  part  of  the  bac- 
teria ;  so  that  through  the  agency  of  the  soap  and  the 
boiling  water  the  milk  receptacles  are  pretty  thoroughly 
cleaned.  Glass  vessels  are  more  satisfactory  than  others, 
since  it  is  much  easier  to  tell  whether  they  are  clean. 
Glass,  however,  is  easily  broken  in  hot  water,  and  care 
must  be  taken  in  the  cleaning. 

3.  Temperature.  The  effect  of  temperature  upon  the 
keeping  of  milk  is  more  striking  than  upon  that  of  any 
other  food  product.  Since  milk  may  be  frozen,  it  may  be 
kept  in  that  condition  for  weeks,  months,  or  even  years 
without  change.  It  is  rarely  possible  to  preserve  milk  in 
this  way,  however,  although  freezing  has  recently  been 
adopted  in  some  communities  as  a  means  of  furnishing 
fresh  milk  to  the  public.  But  other  means  of  cooling  are 
in  constant  use.  Milk  is  frequently  placed  in  a  cellar,  since 
the  temperature  is  lower  than  in  the  rest  of  the  house. 
Another  widely  adopted  plan  is  to  lower  the  milk  into  a 
well,  where,  since  it  is  near  the  water,  it  is  cooled.  An 
even  more  practical  and  widely  used  device  is  the  ice 
chest,  in  which  low  temperature  can  be  easily  maintained. 
The  lower  the  temperature  the  better  the  results,  and  con- 
sequently the  more  ice  used  the  better.  The  ice  chest  has 


IQO  BACTERIA,  YEASTS,  AND   MOLDS 

become  a  practical  necessity  for  families  who  try  to  keep 
milk  for  even  a  few  hours  in  hot  weather.  If  not  cooled, 
milk  will  sour  very  rapidly.  In  a  moderately  warm  room  it 
will  keep  for  a  few  hours  only,  and  in  summer  it  will  some- 
times sour  almost  as  soon  as  delivered  to  the  customer. 
The  housewife  should,  therefore,  place  the  milk  in  as  cold 
a  place  as  she  can  find  immediately  after  receiving  it  from 
the  milkman. 

One  caution  must  be  given  in  regard  to  milk  preserved 
at  low  temperatures.  If  milk  is  put  in  an  ice  chest 
with  a  temperature  in  the  vicinity  of  40°,  it  may  keep 
for  many  days  or  even  weeks  without  souring.  It  is 
usually  assumed  that  milk  is  perfectly  good  and  whole- 
some so  long  as  it  is  not  sour.  This  is  based  upon  the 
assumption  that  the  only  important  change  to  be  feared 
is  souring  ;  so  that  if  it  is  not  sour  it  is  almost  universally 
regarded  as  wholesome.  Nothing  could  be  further  from 
the  truth,  for,  although  the  lactic  bacteria  do  not  grow  at 
low  temperatures,  certain  other  species  do  grow  readily 
enough.  Milk  kept  in  an  ice  chest  for  many  days,  even 
though  perfectly  sweet  and  showing  no  trace  of  souring 
or  curdling,  usually  contains  great  numbers  of  bacteria. 
The  bacteria  that  grow  under  these  circumstances  are 
likely  to  be  more  injurious  to  health  than  the  lactic  bac- 
teria. The  latter  are  not  injurious,  although  they  render 
the  milk  unpleasant  ;  while  the  bacteria  that  grow  at  low 
temperatures  are,  some  of  them  at  all  events,  mischie- 
vous forms,  and  the  milk  may,  therefore,  be  made  very 
unwholesome  by  them.  If  any  unusual  smell  or  taste 
should  appear  in  milk  which  has  been  kept  for  a  day  or 
two  in  an  ice  chest,  it  is  not  fit  to  drink,  for  this  means 


STERILIZATION   OF   MILK  191 

that  unusual  types  of  bacteria  have   developed   to  great 
extent  and  have  probably  made  it  unwholesome. 

4.  Use  of  Preservatives.      The  facts  given  elsewhere 
concerning  the  use  of  preservatives  apply  equally  in  the 
case  of  milk.     The  use  of  any  preservative  is  always  to 
be  deprecated,  and,  so  far  as  concerns  the  housewife,  the 
rule  should  be  that  no  preservatives  should  ever  under 
any  circumstances  be  used  in  milk. 

It  should  be  borne  in  mind  that  none  of  these  devices 
remove  dangerous  disease  germs.  They  make  it  pos- 
sible to  keep  the  milk  longer,  but  do  not  make  it  more 
wholesome  if  it  chances  at  the  outset  to  contain  any 
mischievous  bacteria. 

5.  Sterilization.      Sterilization    of    milk    has    become 
extremely  common  in  the  last  fifteen  years.      It  has  been 
recommended  widely  by  physicians,  it  has  been  introduced 
by  milk-supply  companies,  and  it  has  very  frequently  been 
adopted  in  private  families.     In  our  large  cities,  during 
hot  weather,  families  unable  to  obtain  ice  protect  their 
milk  by  heating  it.     The  most  common  method  is  that 
of  simple  boiling,  a  boiling  temperature  being  sufficient 
to  kill  most  of  the  bacteria  present.     Not  all  of  the  bac- 
teria are  killed   by  this  method,  and  hence  the  milk  is 
not  strictly  sterilized,  for  this  term  means  the  destruc- 
tion of  all  bacteria.      But  the  boiling  does  destroy  most 
of  them,  and  since  it  is  an  extremely  easy  method  to  use, 
the  boiling  of  milk  is  a  very  general  practice.     Absolute 
sterilization  is  possible  by  using  a  heat  higher  than  that  of 
boiling,  but  this  cannot  be  done  in  the  ordinary  kitchen. 
In  common  use  sterilizing  simply  means  boiling,  and  we 
$hall  so  use  the  word,  although  it  is  not  strictly  correct, 


192  BACTERIA,  YEASTS,  AND    MOLDS 

The  purpose  of  sterilization  is  twofold,  (i)  It  delays 
the  souring  of  the  milk.  Milk  that  has  been  boiled  may 
keep  from  souring  for  several  days,  whereas  without  boil- 
ing it  will  keep  only  a  few  hours.  With  the  poorer  fami- 
lies in  cities  this  is  the  chief  purpose  of  boiling  the  milk, 
since  it  will  not  keep  more  than  a  few  hours  without  ice, 
and  they  have  no  ice  chests  where  it  can  be  preserved 
from  souring.  (2)  The  destruction  of  disease  germs.  Milk 
is  a  common  means  by  which  certain  contagious  diseases 
are  distributed  through  a  community.  The  diseases  in 
question  are  produced  by  bacteria  in  the  milk,  and  boiling 
destroys  them.  This  is  the  ground  upon  which  physicians 
and  health  boards  have  in  the  past  few  years  so  widely 
advocated  the  boiling  of  milk  that  is  to  be  used  for  drink- 
ing. Since  boiling  does  destroy  practically  all  the  disease 
germs  liable  to  be  in  milk,  it  makes  it  incapable  of  dis- 
tributing contagious  diseases. 

There  are  certain  disadvantages  in  boiling  milk.  The 
taste  is  wholly  changed,  for  boiled  milk  is  quite  a  different 
article  from  raw  milk.  Most  people  do  not  enjoy  the 
taste  of  boiled  milk,  and  the  adoption  of  sterilizing  or 
boiling  will,  therefore,  greatly  reduce  the  amount  of  milk 
used  as  a  food.  It  might  indeed  be  possible  to  learn  to 
enjoy  the  taste  of  boiled  milk.  Children  brought  up  on 
it  like  it,  while  they  cannot  tndure  the  taste  of  raw  milk. 
A  more  serious  objection  to  sterilization  is  that  the  heating 
so  changes  the  nature  of  the  milk  that  it  is  less  easily 
digested  and  assimilated.  Boiled  or  sterilized  milk  can 
be  digested  and  assimilated  readily  enough  by  persons 
with  strong  digestive  powers,  and  many  children  are  satis- 
factorily brought  up  on  it ;  nevertheless  it  is  somewhat 


PASTEURIZATION   OF    MILK  193 

more  difficult  to  digest  and  assimilate  than  raw  milk,  and 
frequently  children  with  weak  digestive  powers  do  not 
flourish  when  fed  upon  such  milk.  This  is  a  serious 
matter  and  has  prevented  the  widely  extended  use  of 
sterilized  milk.  Because  of  these  objections  the  practice 
of  sterilizing  has  not  increased  in  the  last  few  years  as  it 
was  once  believed  it  would. 

6.  Pasteurization.  —  The  objections  to  boiling  have  led 
to  the  adoption  of  a  different  method  of  treating  milk  for 
the  purpose  of  accomplishing  the  same  results.  Pasteur- 
izing is  also  dependent  upon  the  use  of  heat,  but  a  lower 
degree  than  that  of  boiling  is  used.  The  temperature 
adopted  for  this  purpose  is  commonly  between  155°  and 
170°,  sometimes  running  slightly  above  or  below  these 
limits,  and  the  milk  should  be  kept  at  this  temperature 
from  ten  minutes  to  half  an  hour.  //  must  then  be  cooled 
rapidly. 

It  may  seem  strange  that  the  use  of  a  lower  tempera- 
ture than  boiling  should  be  more  satisfactory  than  boiling. 
The  reasons,  however,  are  simple  enough.  The  bacteria 
which  sour  the  milk  do  not  produce  spores  and  are,  there- 
fore, nearly  all  killed  at  a  temperature  of  155°.  Conse- 
quently pasteurized  milk  will  keep  much  longer  than 
unpasteurized  milk.  Furthermore,  all  disease  germs  that 
are  most  liable  to  be  present  are  also  destroyed  by  this 
low  temperature.  The  diseases  ordinarily  distributed  by 
milk  are  produced  by  bacteria  that  do  not  develop  spores, 
and  a  temperature  of  160°  is  sufficient  to  destroy  such 
bacteria.  Moreover,  the  disagreeable  changes  produced 
by  boiling  do  not  appear  at  the  pasteurizing  temperatures. 
Pasteurized  milk  does  not  have  the  taste  of  boiled  milk, 


194 


BACTERIA,   YEASTS,  AND   MOLDS 


and  is  nearly  as  easily  digested  and  assimilated  as  raw 
milk;  hence  the  objections  raised  against  sterilization 
do  not  apply  to  pasteurization. 

On  the  other  hand,  there  is  one  practical  objection.  In 
an  ordinary  household  it  is  almost  impossible  to  find  one 
employed  in  the  kitchen  who  can  satisfactorily  use  a  ther- 
mometer, and  it  is  out  of  the  question  to  expect  any  ordi- 
nary servant  to  heat  milk  at  a  temperature  of  160°  for 


FIG.  68.    Apparatus  for  home  pasteurization  of  milk.     The  figure  on 
the  right  shows  method  of  cooling  the  milk  by  running  water. 

half  an  hour.  The  only  way  it  can  be  accomplished  is  by 
some  device  which  will  bring  about  the  result  in  a  simpler 
way.  The  most  convenient  apparatus  for  this  purpose  is 
that  shown  in  Fig.  68.  This  consists  of  a  series  of  bottles 
which  readily  fit  into  cylinders  placed  in  a  larger  vessel. 
This  receptacle  is  to  be  filled  with  boiling  water  and  the 
bottles,  filled  with  milk,  are  placed  in  the  cylinders.  The 
whole  is  set  aside  to  cool.  The  milk  is  warmed  by  the 
hot  water  surrounding  it,  and  the  water  is  at  the  same 
time  cooled  by  the  milk.  The  size  of  the  vessel  is  so 


PASTEURIZATION    OF   MILK  195 

proportioned  to  the  bottles  that,  when  properly  used,  the 
milk  is  heated  to  about  the  temperature  desired  before  it 
begins  to  cool.  The  use  of  this  pasteurizing  apparatus  is 
extremely  simple  and  can  be  followed  satisfactorily  in  any 
kitchen. 

Where  such  an  apparatus  is  not  obtainable  the  same 
object  can  be  accomplished  in  a  still  simpler  way.  Place 
the  milk  in  quart  glass  jars.  Fill  a  pail  with  boiling  water 
and  place  the  jars  of  milk  in  it.  The  amount  of  water 
should  be  such  as  to  come  nearly  up  to  the  top  of  the 
jars.  The  pail  should  then  be  set  aside  to  cool,  and  the 
milk  should  be  occasionally  stirred.  The  result  is  that 
the  milk  is  warmed  to  about  the  temperature  desired 
before  it  begins  to  cool.  After  the  heating,  the  milk 
should  be  cooled  rapidly  by  running  cold  water  into  the 
pail,  this  step  being  as  important  as  the  heating. 

Pasteurization  has  been  adopted  widely  in  the  last  few 
years  and  its  use  is  increasing.  It  is  possible  to  purchase 
pasteurized  milk  at  the  present  time  in  many  of  the  larger 
cities.  Milk-supply  companies  frequently  adopt  the  prac- 
tice of  pasteurizing  milk  on  a  large  scale  and  furnishing 
it  to  their  customers.  Pasteurization  is  also  extremely 
useful  in  the  household  where  milk  is  used  for  food,  espe- 
cially where  there  are  children.  It  is  certainly  not  safe  at 
the  present  time  to  feed  young  children  milk  from  the  ordi- 
nary milk  supply.  Such  milk,  however,  may  be  rendered 
safe  by  pasteurization,  and,  since  this  does  not  materially 
injure  the  ease  of  digestion,  it  is  an  extremely  wise  pre- 
caution to  pasteurize  all  milk  which  is  to  be  used  for 
children,  especially  if  the  source  of  the  milk  is  not  known 
to  be  reliable. 


196  BACTERIA,   YEASTS,  AND   MOLDS 

One  caution  should  be  given  regarding  the  use  of  pas- 
teurized milk :  the  milk  must  be  used  quickly  after  pas- 
teurizing. It  is  true  that  such  milk  may  keep  for  two 
days  without  difficulty,  but  bacteria  are  growing  in  it  all 
the  while,  and  although  the  milk  does  not  sour  it  soon 
becomes  unfit  to  drink.  Hence  pasteurized  milk  must  be 
used  quickly,  at  least  within  twenty-four  hours  from  the 
time  when  it  was  pasteurized,  and  meantime  it  should  be 
kept  cool  just  as  if  it  had  not  been  pasteurized. 

The  most  important  rule  in  regard  to  the  use  of  milk 
in  the  household  is  that  it  should  be  used  fresh.  No  satis- 
factory method  of  keeping  it  can  prevent  all  bacteria  from 
growing,  and  although  the  use  of  ice  and  of  pasteurization 
or  sterilization  may  keep  it  in  a  drinkable  condition  for  a 
day,  two  days,  or  even  longer,  it  is  always  suspicious  after 
it  has  been  kept  for  this  length  of  time.  Milk  is  plenty 
old  enough  by  the  time  it  reaches  the  house,  and  it  should 
therefore  always  be  used  fresh.  It  is  far  better  to  obtain 
it  frequently,  in  small  quantities,  using  it  up  as  soon  as 
possible  after  it  reaches  the  home. 

Above  all  it  should  be  emphasized  that  clean  milk  is 
better  than  pasteurized  milk.  The  proper  procedure  is  to 
obtain  milk  in  good  condition  and  then  pasteurization  is 
unnecessary.  Pasteurization  is  not  a  guard  against  filth, 
but  only  an  unsatisfactory  means  of  destroying  the  dis- 
ease germs  which  may  chance  to  be  in  the  milk  from 
some  source  of  accidental  contamination.  When  young 
children  must  be  fed  upon  cow's  milk  probably  the  only 
safe  procedure  is  to  adopt  home  pasteurization  or  to  use 
concentrated  milk,  unless  one  can  afford  the  expense  of 
purchasing  milk  from  sanitary  dairies. 


PRESERVATION   OF   EGGS  197 

EGGS 

Eggs  prove  to  be  particularly  difficult  to  preserve. 
They  are  sure  to  contain  bacteria  inside  the  shell,  depos- 
ited there  before  the  egg  was  laid.  These  will  in  time 
cause  the  egg  to  spoil.  Eggs  cannot  be  sterilized  by 
heat,  for  this  cooks  them.  Drying,  of  course,  alters  their 
nature.  The  use  of  low  temperatures  will  preserve  eggs 
as  well  as  fruit.  They  may  be  protected  from  actual 
spoiling  for  some  time  by  placing  them  in  some  liquids 
that  keep  away  the  air.  Brine  is  used,  and  water  glass 
is  even  more  successful.  To  use  the  latter,  mix  the  water 
glass  purchased  at  the  drug  store  with  ten  times  its  bulk 
of  water,  and  keep  the  eggs  in  the  mixture.  They  will 
remain  in  a  usable  condition  for  a  long  time,  though  they 
lose  their  fresh  taste.  No  means  are  known  by  which  this 
can  be  preserved. 

EFFECT  OF  BACTERIA  GROWTH  UPON  THE  WHOLESOME- 
NESS  OF  FOOD 

The  question  whether  the  growth  of  bacteria  in  the 
food  necessarily  renders  it  unwholesome  remains  yet  to 
be  considered.  It  is  evident  that  after  any  food  material 
has  become  completely  putrefied  it  is  quite  ruined  for  all 
food  purposes.  The  vile  tastes  and  odors  become  so 
strong  that  no  one  can  relish  food  that  has  entered  the 
later  stages  of  putrefaction.  But  how  about  the  earlier 
stages,  when  the  flavors  and  odors  are  so  slight  as  to 
indicate  that  bacteria  have  only  begun  their  action  ?  In 
other  words,  are  we  liable  to  eat  food  which  has  begun 


198  BACTERIA,   YEASTS,  AND   MOLDS 

to  be  decomposed  by  bacteria,  and  if   so,  is  such  food 
unwholesome  in  any  respect  ? 

We  cannot  regard  any  material  as  harmful  simply 
because  it  is  a  product  of  decomposition  or  contains  such 
products.  A  number  of  such  decomposition  products  are 
in  more  or  less  constant  use.  Alcohol  is  in  a  sense  a 
decomposition  product  of  yeast.  It  certainly  is  used  to 
a  very  large  extent,  and  probably,  when  used  only  in  small 
quantity,  causes  no  very  considerable  injury.  Vinegar 
is  also  a  decomposition  product  of  bacteria,  and  is  used 
freely  by  the  human  race  without  injury.  The  flavors 
of  our  high-priced  butter  are  due  to  bacteria,  and  the 
extremely  valuable  flavors  of  cheeses  are  due,  in  many 
cases  and  perhaps  in  all,  to  decomposition  products  devel- 
oped in  the  curd  of  milk  by  the  action  of  certain  micro- 
organisms. Sauerkraut  is  a  preparation  which  is  allowed 
to  undergo  an  incipient  decomposition  the  flavors  of  which 
give  the  peculiar  character  to  this  food.  That  sauerkraut 
is  a  harmless  food  product  is,  of  course,  perfectly  evident. 
In  the  general  class  of  flavors  known  as  gamyvto.  have  fla- 
vors of  decomposition  produced  by  microorganisms.  The 
very  common  use  of  such  partially  decomposed  meats,  and 
the  fact  that  many  persons  are  exceptionally  fond  of  them, 
are  indications  enough  that  they  are  not  appreciably  harm- 
ful. These  illustrations  are  sufficient  to  show  that  the 
simple  fact  that  food  contains  decomposition  products 
is  not  sufficient  to  make  it  unwholesome,  since  many 
decomposition  products  are  distinctly  desirable  in  our 
foods.  The  flavors  of  cheese  in  particular  are  very  use- 
ful, for  when  eaten  with  coarse  bread  they  give  relish 
to  otherwise  rather  tasteless  foods. 


PTOMAINE   POISONING  199 

BACTERIAL  POISONS  IN  FOODS 

But,  on  the  other  hand,  there  are  unquestionably  some 
such  products  which  are  harmful  and  which,  even  though 
present  in  small  quantity,  may  be  decidedly  harmful,  or 
even  poisonous.  When  certain  kinds  of  microorganisms 
grow  in  food  material  they  give  rise  to  a  class  of  decom- 
position products  which  have  been  known  under  the  gen- 
eral name  of  ptomaines.  These  ptomaines  are  chemical 
bodies  of  great  complexity  with  whose  chemical  nature  we 
are  not  in  this  work  concerned.  It  is  sufficient  for  our 
purpose  to  know  that  they  are  usually  the  result  of  bac- 
teria growing  in  animal  products,  and,  while  some  of  them 
are  quite  harmless,  others  are  of  an  intensely  poisonous 
nature.  If  such  bodies  develop  in  food  they  may  render  it 
unwholesome,  or  even  fatally  poisonous.  To  such  poison- 
ous decomposition  products  are  due  instances  of  poison- 
ing from  eating  cheese,  quite  a  number  of  which  are  on 
record.  A  similar  cause  explains  the  still  larger  number 
of  cases  of  ice-cream  poisoning,  when  many  people  have 
been  rendered  seriously  and  even  fatally  sick  by  the  eat- 
ing of  ice  cream.  Similar  effects  have  sometimes  resulted 
from  the  use  of  milk,  although  such  cases  are  rare.  Many 
cases  of  poisoning  are  recorded  from  the  use  of  meats,  fish, 
and  sometimes  other  foods. 

The  poisoning  in  all  such  cases  must  not  be  confused 
with  diseases  produced  by  bacteria.  Sometimes  food  may 
contain  disease  germs,  and  these  may  enter  the  body  when 
the  food  is  swallowed,  and  by  growing  inside  of  our  bodies 
produce  disease.  (See  Chapter  XIV.)  But  in  cases  of 
poisoning  from  eating  food  the  bacteria  grow  simply  in 


200       BACTERIA,  YEASTS,  AND  MOLDS 

the  food.  They  do  not  live  in  the  body,  nor  do  they  pro- 
duce any  definite  bacterial  disease.  The  effects  are  due 
simply  to  the  products  of  decomposition  which  have  been 
developed  in  the  foods  by  certain  kinds  of  bacteria. 

These  troubles  are  much  more  common  than  we  are  apt 
to  realize.  Since  bacteria  grow  best  at  high  temperatures, 
it  is  not  surprising  to  find  more  cases  of  food  poisoning  in 
warm  weather.  It  is  not  an  infrequent  occurrence  to  have 
a  general  poisoning  follow  any  one  of  the  innumerable 
banquets  held  in  our  communities.  Hundreds  of  cases 
of  intestinal  trouble  occasionally  follow  such  banquets. 
The  illnesses  resulting  are  rarely  serious,  but  temporarily 
they  produce  great  inconvenience  and  trouble.  They  are 
due  to  the  development  of  ptomaines  in  some  food  prod- 
ucts, since  almost  any  of  the  putrescible  foods  which  come 
upon  our  tables  may,  in  warm  weather  and  under  certain 
circumstances,  undergo  a  type  of  putrefaction  which  gives 
rise  to  these  poisonous  ptomaines.  When  this  occurs  pto- 
maine poisoning  is  quite  likely  to  follow  the  use  of  the 
foods.  Such  ptomaines  are  known  to  be  developed  quite 
readily  in  materials  that  have  been  preserved  in  cold  stor- 
age and  then  removed  to  warm  rooms.  Hence  it  is  desir- 
able to  consume  cold-storage  material  as  soon  as  possible. 
It  is  almost  certain  that  a  large  part  of  the  summer 
diarrhoea  so  common  in  warm  weather  is  due  to  poison- 
ous decomposition  products  developed  in  some  of  our  foods, 
milk  being  particularly  likely  to  cause  such  trouble. 

Unfortunately  we  know  very  little  concerning  the  con- 
ditions under  which  such  poisonous  materials  appear. 
Not  all  bacteria  produce  them,  and  it  is  only  rarely  that 
food  is  thus  rendered  unwholesome  by  bacteria.  We 


PTOMAINE   POISONING  2OI 

know  that  strictly  fresh  foods  never  contain  these  poisons. 
We  know  that  their  development  is  dependent  in  a  measure 
upon  temperature,  inasmuch  as  they  do  not  develop  in  food 
that  is  kept  cool.  We  know  that  decomposition  products 
are  more  likely  to  give  rise  to  poisonous  ptomaines  in  the 
absence  of  oxygen  than  in  its  presence.  We  know,  lastly, 
that  injurious  substances  are  produced  by  bacteria;  but 
we  do  not  yet  know  the  source  of  the  bacteria,  nor  have 
we,  for  this  reason,  discovered  any  methods  for  keeping 
them  from  our  foods  other  than  those  ordinarily  adopted 
for  checking  bacterial  growth.  Anything  that  will  pre- 
vent bacteria  from  growing  will  prevent  ptomaine  poison- 
ing. Consequently  low  temperature,  drying  of  foods,  and 
the  other  devices  already  suggested  are  the  only  means  we 
have  for  guarding  ourselves  from  such  troubles.  We  may 
wisely  remember  that  ptomaine  poisoning  is  most  likely 
to  occur  in  foods  that  have  been  kept  for  some  time  in  a 
moderately  warm  temperature.  Fresh  foods  never  contain 
poisonous  ptomaines. 

The  use  of  fresh  foods  and  the  preservation  at  low  tem- 
peratures of  any  food  that  must  be  kept  for  some  time  are 
the  only  rules  that  can  be  given  at  present  for  prevent- 
ing such  instances  of  poisoning.  Eat  food  fresh  when 
possible  ;  keep  it  cold  if  it  must  be  preserved ;  do  not 
keep  it  any  longer  than  necessary,  and  be  particularly 
careful  to  consume  quickly  any  material  taken  from  cold 
storage.  When  food  begins  to  have  the  smell  of  decom- 
position, it  becomes  suspicious,  although  this  does  not 
mean  that  it  is  necessarily  dangerous,  since  many  of  these 
decomposition  products  are  quite  harmless.  The  food 
product  that  seems  to  give  the  largest  amount  of  trouble  is 


202  BACTERIA,   YEASTS,  AND   MOLDS 

ice  cream,  and  it  is  therefore  desirable  to  be  particularly 
on  one's  guard  against  its  use  in  warm  weather  and,  if 
possible,  to  use  only  that  which  has  been  made  from  fresh 
materials.  Since  the  dangers  are  greatest  in  summer  we 
should  be  particularly  careful  at  this  season  not  to  allow 
any  putrescible  food  to  be  warmed  by  the  sun  or  by 
standing  near  a  stove. 


CHAPTER    XIV 
DISEASE    BACTERIA 

The  bacteria  hitherto  studied  are  all  saprophytes.  There 
remain  for  consideration  those  that  can  carry  on  their  life 
within  the  body  of  living  animals  and  plants,  namely,  the 
parasites.  The  distinction  between  parasites  and  sapro- 
phytes is  not  a  sharp  one,  for  while  some  species  can  live 
only  in  lifeless  material,  and  others  only  in  living  material, 
there  are  many  that  can  live  either  a  parasitic  or  sapro- 
phytic  life.  When  the  bacteria  grow  in  the  body  of  a 
living  animal  or  plant,  they  may  give  rise  to  disease,  and 
these  parasitic  bacteria  are  therefore  called  disease  germs, 
pathogenic  bacteria,  disease  bacteria,  etc. 

How  BACTERIA  PRODUCE  DISEASE 

The  parasitic  bacteria  are  all  capable  of  growing  and 
multiplying  in  the  body,  but  the  habits  of  different  species 
of  disease  bacteria  are  widely  different.  Sometimes  they 
become  distributed  all  over  the  body,  developing  rapidly  in 
any  part,  perhaps  even  in  the  blood.  In  such  cases  the 
disease  produced  by  them  is  not  located  at  any  particular 
point,  but  distributed  all  through  the  body.  This  is  true 
of  certain  forms  of  so-called  blood  poisoning,  or  septiccemia. 
On  the  other  hand,  it  sometimes  happens  that  the  micro- 
organisms become  located  in  very  definite  parts  of  the 

203 


204  BACTERIA,   YEASTS,  AND    MOLDS 

body,  and  while  able  to  grow  in  certain  places  are  unable 
to  grow  elsewhere.  In  these  cases  the  disease  produced 
may  be  local,  although  secondary  general  symptoms  may 
appear,  as  is  true  of  diphtheria.  Between  these  two 
extremes  are  many  intermediate  types. 

Whenever  bacteria  obtain  a  foothold  in  the  body  they 
multiply  more  or  less  rapidly,  and  have  the  same  general 
power  of  forming  decomposition  products  and  secretions 
as  they  have  when  growing  in  lifeless  food.  These  new 
substances  arising  in  the  body  are  as  varied  in  nature  as 
are  those  produced  by  the  common  saprophytes.  Among 
them  are  almost  sure  to  be  some  that  are  distinctly  poi- 
sonous, which  we  call  toxins.  These  toxins  may  be  either 
decomposition  products  or  bacterial  secretions  ;  but  how- 
ever they  are  produced  they  are  liable  to  be  absorbed 
by  the  blood,  and  the  body  may  thus  be  directly  poi- 
soned by  them.  If  the  bacteria  are  in  the  blood  itself, 
this  poisoning  is  easy  to  understand ;  but  localized  dis- 
eases are  similarly  explained.  Diphtheria,  for  example,  is 
produced  by  bacteria  growing  on  the  inside  surface  in  the 
throat.  The  bacteria  themselves  do  not  enter  the  body, 
but  their  excretions  are  absorbed  rapidly  enough.  Grow- 
ing in  the  throat,  the  bacteria  develop  very  powerful 
toxins,  and  these  are  absorbed  from  the  throat  into  the 
blood,  producing  a  general  poisoning  of  the  whole  body. 
Sometimes  the  germs  grow  in  the  intestine  (Asiatic  chol- 
era), and  their  poisonous  secretions  are  absorbed  with  the 
digested  food.  Something  similar  is  true  of  practically  all 
disease  germs.  All  produce  poisonous  materials  which  are 
absorbed  by  the  body,  and  these  cause  the  direct  injury 
characteristic  of  the  various  diseases. 


DISEASES,   HOW   PRODUCED  205 

Not  all  the  bacteria  which  secrete  poisons  are  disease 
germs.  Some  saprophytes  may  produce  deadly  poisons, 
but  since  they  are  not  able  to  grow  in  the  living  body 
they  are  never  in  a  proper  sense  the  causes  of  disease. 
They  might,  however,  grow  in  our  food  and  render  that 
poisonous,  so  that  if  it  were  subsequently  eaten  it  would 
give  rise  to  cases  of  food  poisoning  such  as  already 
noticed.  Such  troubles  are  cases  of  toxic  poisoning  but 
not  true  diseases.  A  true  germ  disease  is  caused  by 
the  germs  themselves  entering  and  multiplying  within 
the  body.  When  the  poisons  and  not  the  bacteria  are 
absorbed  by  the  body,  the  sickness  comes  on  very  quickly 
and  violently,  —  a  few  hours  after  the  poisonous  food  is 
consumed.  But  it  is  also  of  short  duration,  for,  if  the 
amount  of  poison  absorbed  is  not  sufficient  to  produce 
death,  it  is  quickly  excreted  from  the  body,  and  a  clay  or 
two  afterward  the  person  will  have  perfectly  recovered, 
except  for  the  weakening  effects  of  the  poisoning.  This 
is  the  general  history  of  cases  of  poisoning  from  ice  cream, 
etc.  A  true  disease  acts  very  differently.  It  is  slow  in 
appearing,  gradual  in  its  development,  and  very  slow  in 
disappearing. 

The  Course  of  Bacterial  Diseases.  The  diseases  pro- 
duced by  bacteria  have  different  histories  in  the  body ; 
but  a  considerable  number  of  them,  with  many  of  which 
the  housewife  is  intimately  concerned,  have  a  course  some- 
what as  follows.  For  some  days  after  the  bacteria  enter 
the  body  they  have  difficulty  in  maintaining  a  foothold. 
Sometimes,  indeed,  even  though  they  succeed  in  entering, 
they  are  driven  out  by  resisting  powers  which  the  body 
possesses  but  which  we  cannot  here  particularly  consider. 


206       BACTERIA,  YEASTS,  AND  MOLDS 

If,  however,  they  overcome  these  resisting  forces  and  gain 
a  foothold,  they  then  begin  to  develop,  so  that  in  the 
course  of  a  few  days  they  become  quite  numerous.  As 
they  grow  they  produce  their  toxins,  and  these,  devel- 
oped at  first  in  small  quantity,  are  absorbed  by  the  body 
and  give  rise  to  the  first  slight  symptoms  characteristic 
of  the  particular  disease.  But  the  bacteria  continue  to 
multiply  and  produce  their  poisons  in  greater  and  greater 
abundance.  As  a  natural  consequence  the  body  becomes 
more  and  more  influenced  by  them,  the  symptoms  of  the 
disease  become  more  and  more  violent,  the  person  becomes 
more  and  more  ill.  This  continues  until  death  occurs  or 
a  crisis  is  reached.  After  the  crisis  the  bacteria  begin  to 
disappear,  and  are  finally  driven  from  the  body,  while  the 
poisons  they  produced  become  less  capable  of  causing 
injury  and  are  eventually  excreted.  The  person  may  then 
recover  entirely  from  the  attack. 

RESISTANCE  AGAINST  DISEASE 

In  most  cases  the  body  in  driving  off  the  bacteria 
acquires  the  power  of  guarding  itself  from  a  second  attack 
of  the  same  species,  and  the  individual,  for  a  time  at  least, 
is  not  liable  to  a  second  attack  of  the  same  disease.  The 
whole  explanation  of  how  the  body  protects  itself,  drives 
off  the  invading  bacteria,  counteracts  their  toxins,  and 
retains  this  power  of  protection  in  the  future,  is  one  of 
the  interesting  problems  upon  which  bacteriologists  are 
still  studying.  We  cannot  here  enter  into  the  subject,  but 
it  is  well  to  remember  that  a  recovery  from  common  con- 
tagious diseases,  like  smallpox,  scarlet  fever,  measles,  mumps, 


DISEASE   BACTERIA  2O/ 

whooping  cough,  diphtheria,  grippe,  tonsilitis,  typhoid  fever, 
etc.,  protects  the  individual  for  a  time  from  a  second  attack. 
The  protection  lasts  much  longer  in  some  cases  than  in 
others,  and  whereas  the  protection  against  the  diseases  at 
the  beginning  of  the  above  list  lasts  for  years  or  for  life, 
the  protection  against  those  at  the  end  of  the  list  lasts 
for  only  a  few  months  or  weeks. 

Two  important  facts  in  regard  to  the  resistance  against 
disease  must  be  mentioned.  The  ability  of  a  person  to 
resist  an  attack  of  any  kind  of  disease  germ  is  dependent 
upon  two  things. 

1.  The  vigor  of  the  bacteria.     It  has  been  learned  by 
experience  that  the  bacteria  reproducing  any  definite  dis- 
eases are  more  vigorous  at  some  seasons  than  at  others. 
A  very  vigorous  lot  of  bacteria  will  give  rise  to  a  more 
serious  attack  of  the  disease,  and  will  be  more  difficult  to 
drive  out  than  a  lot  of   the  same  kind  of  bacteria  that 
have  been  weakened  by  some   unknown  conditions.     It 
is  a  well-known  fact   that  some  epidemics  of  smallpox, 
measles,  etc.,  are  milder  than  others  ;  not  simply  because 
fewer  people  are  attacked,  but  because  those  who  are  sick 
have  the  disease  in  a  milder  form.     This  difference  in  the 
severity  of  the  attack  is  due  in  part  to  a  difference  in 
the  vigor  and  activity  of  the  bacteria  that  make  entrance 
into  the  body,  and  is  a  matter  beyond  our  control. 

2.  The  vigor  of  the  body  itself.     A  vigorous,  healthy, 
active  body  has  a  power  of  resistance  sufficient  to  drive  off 
most  kinds  of  these  invading  parasites.      If,  however,  the 
body  is  less  vigorous,  less  active,  i.e.  in  a  low  state  of 
physical  health,  its  resisting  power  is  less  and  the  body  has 
great  difficulty  in  driving  off  the  invaders.     This  resisting 


208       BACTERIA,  YEASTS,  AND  MOLDS 

power,  then,  depends  upon  the  vigor  of  the  physical 
health.  Hence  it  is  of  the  greatest  practical  importance 
for  every  one  to  remember  that  robust  physical  health  is 
the  best  protection  against  many  types  of  disease  due  to 
the  invasion  of  bacteria.  It  is  true  that  persons  in  appar- 
ently perfect  health  may  take  these  diseases,  but  it  is  never- 
theless the  rule  that  the  stronger  the  physical  vigor  the 
less  is  the  likelihood  of  being  attacked.  At  any  rate  a 
person  of  strong  constitution  will  have  a  milder  attack  of 
the  disease  than  one  whose  physical  activity  is  weakened. 

DISTRIBUTION  OF  CONTAGIOUS  DISEASES 

While  these  problems  are  of  the  utmost  importance  in 
every  household,  hygiene  does  not  properly  belong  to 
the  study  of  bacteria.  There  is  one  phase  of  the  subject 
of  bacterial  diseases,  however,  that  is  of  vital  interest  to 
every  housewife.  If  contagious  diseases  are  due  to  the 
growth  of  bacteria  or  other  microorganisms,  it  is  clear 
that  they  may  be  avoided  if  we  can  prevent  the  disease 
germs  from  reaching  the  healthy  individual.  We  have 
already  noticed  how  one  bit  of  decaying  fruit  contaminates 
another,  the  spores  passing  to  the  perfect  fruit  and  caus- 
ing that  also  to  decay.  We  have  seen  how  the  minute 
spores  of  molds  and  yeasts  are  scattered  through  the  air 
and  blown  about  by  the  winds  until  they  are  almost  sure 
to  be  found  everywhere.  We  have  noticed,  also,  how 
readily  bacteria  are  distributed,  and  how  surely  the  air 
of  our  houses  is  filled  with  them.  We  have  learned  that 
these  microorganisms  are  so  abundant  in  the  air  that  they 
are  sure  to  get  into  any  exposed  bit  of  food,  and  we  have 


DISTRIBUTION    OF   CONTAGIOUS   DISEASES      209 

seen  that  one  of  the  housewife's  duties  is  to  protect  her 
food  from  their  action. 

Very  similar  but  more  serious  problems  arise  in  the 
household  in  connection  with  the  distribution  of  disease 
germs.  If  a  disease  is  produced  only  by  the  development 
of  bacteria,  of  course  it  may  be  prevented  if  we  can 
discover  some  means  of  keeping  the  disease  bacteria 
from  the  body.  In  canning  fruit  the  housewife  tries  to 
prevent  bacteria  from  reaching  it.  Can  she  not  by  a 
similar  principle  protect  her  children  from  contagious 
diseases  ?  This  problem  is  the  one  feature  of  contagious 
diseases  that  belongs  primarily  to  the  housewife.  The  pre- 
vention of  the  distribution  of  such  diseases  is  a  subject 
which  the  physician  can  handle  only  indirectly,  because 
it  depends  upon  conditions  in  the  home  which  he  can- 
not control.  The  modern  trained  nurse  may  be  able  to 
do  this ;  but  in  the  majority  of  cases  the  whole  problem 
of  the  prevention  of  the  distribution  of  contagious  dis- 
eases from  individual  to  individual  must  rest  upon  the 
home  maker.  The  doctor  comes  in  for  a  few  moments 
only,  the  nurse  is  only  occasionally  at  hand,  and  the  duty 
of  protecting  the  inmates  of  the  home  from  disease  must 
fall  upon  the  one  who  is  at  the  head  of  it.  To  do  it  she 
must  proceed  according  to  the  same  principles  by  which 
she  protects  her  food  from  decay.  As  she  is  obliged  to 
use  devices  to  keep  bacteria  away  from  all  putrescible  food 
materials,  and  as  she  must  keep  decaying  apples  away 
from  the  perfect  ones,  so  it  is  her  duty  to  guard  the  mem- 
bers of  her  family  from  the  invasion  of  the  disease  germs. 

In  her  battle  against  disease  the  housewife  should 
remember  three  things. 


210  BACTERIA,   YEASTS,  AND    MOLDS 

1 .  The  causes  of  these  diseases  are  real  tilings  and  not 
simply  matters  of  imagination.     They  can  be  seen  with 
the  microscope ;  they  feed ;  they  grow  and  multiply  like 
larger  animals  and  plants.     Contagious  diseases  are  not 
mere  nervous  affections  that  may  be  banished  by  forget- 
ting them  and  believing  in  their  nonexistence.     They  are 
produced  by  definitely  known  living  beings,  and  can  be 
avoided  only  by  keeping  our  bodies  free  from  them. 

2.  The  causes  of  the  diseases  in  question  are  always 
microscopic,  and  can  never  be  detected  by  the  naked  eye. 
Material  which  cannot  be  seen  may  therefore  be   filled 
with  microscopic  parasites  which  are  capable  of  producing 
fatal  diseases.     An  invisible  particle  of  dust  may  harbor 
numbers  of  deadly  germs  ready  to  invade  the  living  body 
and  produce  trouble.     Since  the  foes  cannot  be  seen,  the 
battle  is  a  blind  and  therefore  a  difficult  one. 

3.  These  agents  are  alive ;   they   grow  and   multiply. 
Thus    it    follows    that    infectious    material    may    rapidly 
increase  in  quantity.     A  particle  of  dust  containing  only 
a  few  parasitic  bacteria  may  be  the  starting  point  of  a 
disease  which  may  spread  widely  until  it  shall  become  an 
epidemic  with  its  scores  of  victims.     The  problem  to  be 
dealt  with  is  something  like  that  of  fire.     The  flame  of 
a  single  match  is  very  slight  and  may  do  little  injury ; 
but  this  same  flame  may  start  a  conflagration  that  will 
burn  an  entire  city.     So  with  the  disease  bacteria.     Each 
of  them,  although  extremely  minute,  is  capable  of  develop- 
ing with  wonderful  rapidity,  and  a  single  one  may  develop 
sufficiently  in  the  course  of  a  few  days  to  be  scattered 
far  and  wide,   causing  a  great  epidemic.     The   extreme 
minuteness  of  these  foes  and  their  wonderful  power  of 


DISTRIBUTION   OF   CONTAGIOUS   DISEASES     211 

multiplying  are  the  most  prominent  facts  to  be  borne  in 
mind  when  contending  with  contagious  diseases.  We 
must  not,  therefore,  think  that  anything  is  safe  from 
contamination  with  bacteria  because  it  looks  clean.  The 
eye  may  not  see  the  contamination  even  when  it  is  present. 
Clear,  sparkling  water  may  sometimes  contain  deadly  bac- 
teria, while  dirty  water  may  be  perfectly  safe  to  drink. 
Nor  must  we  think  any  substance  safe  because  it  has  only 
an  extremely  small  quantity  of  infectious  material  upon  it, 
for  bacteria  can  grow  so  rapidly  that  a  half  dozen  may 
become  millions  in  a  few  hours  if  they  have  a  chance 
to  feed  arid  grow. 


CHAPTER    XV 

PREVENTION    OF    DISTRIBUTION    OF    CONTAGIOUS 
DISEASES 

What  are  the  diseases  against  which  the  housewife  must 
be  on  her  guard  lest  they  distribute  themselves  through 
her  home?  They  are  evidently  those  due  to  microscopic 
parasites,  either  bacteria  or  other  forms  of  living  things. 
Not  all  forms  of  sickness  are  due  to  parasites,  for  some 
have  an  entirely  different  cause.  But  the  diseases  with 
which  we  are  here  concerning  ourselves  —  the  so-called 
contagious  diseases,  which  are  well  known  to  be  "  catch- 
ing "  and  which  pass  from  the  patient  to  a  healthy  indi- 
vidual—  are  due  to  parasites. 

The  chief  of  these  diseases  are  smallpox,  scarlet  fever, 
diphtheria,  measles,  mumps,  whooping  cough,  tonsilitis,  and 
influenza  or  grippe, — all  known  to  be  contagious.  In  addi- 
tion there  are  other  diseases,  serious  but  much  less  con- 
tagious ;  so  slightly  contagious,  indeed,  that  until  quite 
recently  they  have  not  been  looked  upon  as  being  capable 
of  passing  from  individual  to  individual.  The  most  prom- 
inent and  important  are  typhoid  fever  and  tuberculosis. 
The  best-known  form  of  the  latter  disease  is  commonly 
known  by  the  name  of  consumption.  Formerly  neither 
typhoid  fever  nor  consumption  was  supposed  to  be  con- 
tagious, but  it  is  now  known  that  under  some  conditions 
they  pass  from  patient  to  healthy  individual.  Lastly 
may  be  mentioned  a  class  of  diseases  not  in  any  proper 

212 


CONDITIONS   OF   CONTAGION  213 

sense  contagious  but  produced  by  parasitic  organisms 
which  may  under  peculiar  conditions  pass  from  individ- 
ual to  individual.  Most  prominent  among  this  last  class 
is  malaria,  a  disease  never  known  to  pass  directly  from 
one  person  to  another  but  which  may  be  distributed  from 
individual  to  individual  through  an  agency  to  be  noticed 
presently.  It  must  not  be  assumed  that  science  at  the 
present  time  knows,  the  cause  of  all  the  diseases  here 
listed.  Some  of  them,  like  measles,  scarlet  fever,  whoop- 
ing cough,  and  mumps,  while  almost  certainly  caused 
by  microorganisms  living  in  the  human  body,  have  not 
yet  been  satisfactorily  explained,  and  we  do  not  know 
the  actual  germs  which  cause  them.  There  are  some 
other  contagious  diseases  besides  those  mentioned,  for 
almost  any  trouble  that  produces  open  sores  anywhere 
on  or  in  the  body  is  liable  to  be  distributed  from  person 
to  person.  Those  mentioned  are,  however,  the  most 
important. 

CONDITIONS  OF  CONTAGION 

To  make  it  possible  for  a  disease  to  pass  from  one  person 
to  another,  three  conditions  must  be  fulfilled:  (i)  The 
microorganisms  which  produce  the  disease  must  find  some 
means  of  exit  from  the  patient.  (2)  The  organisms  must  in 
some  way  be  carried  from  the  patient  to  the  healthy  indi- 
vidual. (3)  The  organisms  must  find  some  means  of  enter- 
ing the  body  of  the  healthy  individual.  If  the  parasites 
can  meet  these  three  conditions,  the  disease  will  be  carried 
from  patient  to  well  person,  and  thus  will  be  contagious. 
For  a  proper  understanding,  therefore,  of  the  way  to  han- 
dle contagious  diseases  in  the  home  we  need  to  consider 


214  BACTERIA,   YEASTS,  AND    MOLDS 

these  three  factors.  If  we  know  how  the  bacteria  leave 
the  body  of  the  patient,  how  they  are  distributed,  and  how 
they  enter  the  body  of  another,  we  are  well  equipped  to 
guard  against  them. 

I.    The  Means  of  Elimination  from  the  Body 

A  knowledge  of  the  means  by  which  the  contagious 
material  leaves  the  body  of  the  patient  is  of  first  impor- 
tance in  preventing  the  distribution  of  such  material, 
and  should  always  be  the  first  question  asked.  There 
are  several  different  methods. 

The  parasites  that  produce  certain  diseases  do  not  find 
any  direct  means  of  being  eliminated  from  the  body,  and 
when  this  is  the  case  the  disease  is  not  in  any  proper 
sense  contagious.  Malaria  is  the  best  example  of  this 
class  of  diseases,  and  yellow  fever  is  probably  a  second. 
Malaria,  chills  and  fever,  or  fever  and  ague,  are  all  the 
same  disease,  and  are  produced  by  a  microscopic  parasite 
living  in  the  human  blood.  Growing  there,  it  develops 
poisonous  secretions,  and  these  acting  upon  the  body  give 
rise  to  the  symptom  of  chill  followed  by  fever  only  too 
well  known  in  this  disease.  The  parasite  is  a  minute  little 
body  (Fig.  69,  i)  which  enters  the  blood  corpuscle.  Inside 
this  corpuscle  it  grows,  and  finally  breaks  up  into  many  lit- 
tle bodies,  or  spores.  As  soon  as  the  spores  are  formed 
the  blood  corpuscle  breaks  to  pieces,  setting  the  spores 
free  and  at  the  same  time  liberating  the  secreted  poisons. 
These  poisons  cause  the  chill  followed  by  fever  well 
known  in  malaria.  The  spores  may  then  enter  into  other 
blood  corpuscles  and  go  through  the  same  history  again 


MALARIAL  PARASITES 


(Fig.  69,  1-7).  It  takes  about  forty-eight  hours  for  them 
to  complete  their  history,  and  hence  the  chills,  in  the 
common  form  of  malaria,  occur  every  other  day.  One 


FIG.  69.     Malarial  organism. 

2-7  show  the  stages  that  occur  in  ordinary  blood,  7  representing  the  spores  which  appear 
after  the  blood  corpuscle  breaks  to  pieces.  These  spores  are  like  2  and  immediately 
enter  into  fresh  corpuscles,  as  at  3.  8  shows  a  so-called  crescent  body  in  the  corpuscle. 
The  crescent  bodies  become  the  sexual  bodies,  9  and  ga,  which  develop  in  the  mosquito. 
10  shows  the  union  of  the  female  sex  body,  9,  with  one  of  the  flagella  of  go..  11-15 
show  the  development  of  the  united  mass,  10,  in  the  body  of  the  mosquito,  finally 
producing  spores  such  as  shown  at  i.  16,  the  intestine  of  the  mosquito,  showing  the 
malarial  organism  attached. 

form  of  the  parasites,  however,  requires  three  days  to  com- 
plete the  cycle.  The  malarial  parasites  remain  in  the  blood 
and  never  pass  out  of  the  body  by  any  of  the  ordinary 
excretions.  There  is  therefore  no  direct  means  by  which 


2l6  BACTERIA,  YEASTS,  AND    MOLDS 

they  can  pass  from  one  person  to  another,  and  conse- 
quently malaria  is  not  a  contagious  disease.  This  fact 
has  been  known  for  many  years,  and  no  instances  of 
direct  contagion  have  been  noted. 

The  last  few  years,  however,  have  disclosed  the  fact  that 
there  is  a  means  by  which  malaria  is  transmitted  indi- 
rectly from  man  to  man,  and  have  shown  us  how  the 


FIG.  70.  a,  the  harmless  mosquito  (Culex) ;  b,  the  malarial 
mosquito  (Anopheles),  a'  and  a"  show  the  position  of  the 
harmless  mosquito  when  lighting  on  the  floor  or  on  the 
wall ;  £',  b"  and  b'"  show  the  position  of  Anopheles  when 
lighting  on  the  floor,  wall,  and  ceiling. 

human  body  usually  becomes  infected  with  this  disease.  A 
certain  kind  of  mosquito  (Fig.  70,  b)  forms  an  interme- 
diate connection  between  a  malarial  patient  and  another 
individual.  This  kind  of  mosquito  may  bite  the  patient, 
sucking  into  its  body  at  the  time  a  considerable  quantity 
of  blood.  Inasmuch  as  the  blood  contains  the  malaria  para- 
sites, the  mosquito  will  become  filled  with  them.  The  little 
organisms  live  in  the  mosquito  as  readily  as  they  do  in  the 


MOSQUITOES   AND    MALARIA  217 

human  body,  undergoing  a  different  history,  however.  In 
the  mosquito  they  pass  through  a  new  series  of  changes 
(Fig.  69,  8-15),  finally  lodging  in  the  glands  around  the 
mouth  (salivary  glands).  If  this  mosquito  with  its  sali- 
vary glands  thus  loaded  with  these  little  parasites  chances 
to  bite  another  individual,  thrusting  its  proboscis  in 
through  the  skin,  these  parasites  will  pretty  surely  be 
forced  into  the  body  of  that  individual.  When  the  mos- 
quito flies  away  it  will  leave  the  blood  of  the  one  bitten 
inoculated  with  the  parasites.  They  are  now  in  a  loca- 
tion adapted  to  their  life  and  they  begin  to  develop.  In 
a  few  days  they  are  abundant  enough  to  produce  a  poi- 
sonous effect  upon  their  victim  and  he  develops  an  attack 
of  malaria.  Thus  this  particular  disease  is  transmitted 
from  person  to  person  by  means  of  mosquitoes,  and  at  the 
present  time  it  seems  as  if  most,  and  perhaps  all,  of  the 
cases  of  malaria  start  originally  from  mosquito  bites. 
Malaria  is  most  prevalent  at  the  seasons  of  the  year  when 
mosquitoes  are  abundant ;  it  is  most  abundant  in  parts 
of  the  world  where  mosquitoes  are  most  common ;  and 
it  is  most  likely  to  be  caught  at  night,  the  time  when 
mosquitoes  are  the  liveliest. 

It  should  be  noted,  however,  that  not  all  kinds  of  mos- 
quitoes are  capable  of  carrying  this  malarial  parasite. 
Fortunately  the  most  common  mosquito  is  quite  free 
from  them  and  is,  therefore,  not  a  source  of  danger.  Only 
one  group  of  mosquitoes  is  associated  with  this  trouble. 
Fig.  70,  bt  shows  the  common  form  of  this  species,  and 
also  the  ordinary,  harmless  mosquito,  a.  The  differences 
between  them  are  shown  in  the  figures.  The  most  easily 
distinguished  differences  are  the  five  delicate  hairlike 


2l8       BACTERIA,  YEASTS,  AND  MOLDS 

feelers  on  the  head  of  the  dangerous  species,  rather  than 
three  as  in  the  harmless  form  (Fig.  70,  a  and  b),  and  the 
method  of  lighting  with  the  body  held  in  a  straight  line 
(Fig.  70,  b',  b",  b'")y  rather  than  bent  as  in  the  harmless 
species  (Fig.  70,  a'  and  a").  It  must  also  be  remembered 
that  not  all  mosquitoes,  even  of  the  harmful  species,  will 
be  dangerous.  Only  those  that  have  sucked  the  blood 
from  malarial  patients  will  contain  the  parasites  and  be 
able  to  transmit  the  disease.  In  other  words,  of  all  the 
mosquitoes  that  may  bite  us  in  summer  only  a  few  are 
likely  to  be  infected  and  produce  any  trouble.  We  may 
be  bitten  thousands  of  times  and  still  be  free  from  malaria, 
while  the  next  mosquito  that  bites  us  may  inoculate  us 
with  these  parasites. 

That  family  is  the  best  protected  against  malaria  that 
is  the  best  protected  against  mosquitoes.  If  we  live  in 
a  region  where  malaria  abounds,  it  is  somewhat  dangerous 
to  remain  out  of  doors  during  the  night,  or  even  in  the  early 
part  of  the  evening,  unless  properly  protected.  At  this 
time  mosquitoes  are  most  likely  to  be  flying  about.  From 
this  fact  arises  the  ground  for  belief  that  night  air  is 
dangerous.  It  is  not  the  night  air  but  the  mosquitoes 
in  the  air  that  produce  the  trouble.  It  is  also  evident 
that  the  best  method  of  protecting  a  household  from 
malaria  is  the  use  of  mosquito  netting.  It  is  a  curious 
fact  that  its  use  at  our  windows  and  doors  is  the  best 
protection  from  these  microscopic  parasites,  inasmuch  as 
mosquito  nettings  will  keep  mosquitoes  from  the  houses 
and  will  reduce  the  chances  of  contagion.  This  is  not  a 
matter  of  theory  only,  for  it  has  been  found  by  careful 
observation  and  experiment  that  the  simple  procedure 


ELIMINATION    OF   GERMS   FROM    PATIENTS     219 

of  covering  doors  and  windows  of  houses  with  mosquito 
netting  has  produced  a  marked  decrease  in  the  amount 
of  malaria  in  these  dwellings. 

It  has  been  proved  recently  that  yellow  fever  also  is 
distributed  by  mosquitoes  rather  than  by  direct  personal 
contagion.  The  species  of  mosquito  is  different  from 
either  of  those  shown  in  Fig.  70,  and  lives  only  in  warm 
climates.  Mosquito  netting  is  the  best  check  for  this 
disease.  Yellow  fever  has  been  almost  wholly  stamped 
out  of  Havana  by  simply  surrounding  the  patients  with 
netting,  thus  preventing  the  mosquitoes  from  biting  them 
and  becoming  infected  with  the  germs  which  they  might 
carry  to  other  persons. 

In  all  truly  contagious  diseases  the  parasites  have  some 
means  of  leaving  the  body  of  the  patient.  Their  methods 

of  exit  are  numerous,   but  it  is  not  very 

V         V 
difficult  to  determine,  in  the  case  of  any        fX  jf'^*"' 

particular  disease,   the  methods   by  which        I  **^*  \ 
the  parasites  leave  the  body.     Most  types       .     ^SJ    ' 
of    contagious    diseases     have    suggestive  >k**r 

symptoms.    For  example,  in  smallpox,  scar-  FlG-7l>  Bacillus 

,    ,     -  1^.1  '  ••    ..  °f  diphtheria. 

let  fever,  or  measles,  there  is  an  eruption 
of  the  skin,  and  it  becomes  probable  at  once  that  this 
eruption  is  a  means  of  elimination  of  microorganisms. 
In  diphtheria  (Fig.  71)  the  germs  grow  in  the  mouth, 
clinging  to  the  surfaces  inside  the  mouth  and  throat,  and 
it  is  quite  evident  that  the  breath,  or  at  all  events  the 
forcible  breath  that  comes  with  coughing,  will  detach 
the  bacteria  from  their  position  in  the  throat  and  blow 
them  into  the  air.  In  the  case  of  whooping  cough  the 
violent  paroxysms  of  coughing  are  probably  a  means  of 


220  BACTERIA,  YEASTS,  AND    MOLDS 

eliminating  the  infectious  organisms.  The  same  is  true, 
probably,  of  tonsilitis  and  grippe  (Fig.  72).  In  consump- 
tion, discharges  from  the  lungs  pass  into  the  mouth  and 
are  voided  in  the  sputum.  It  becomes  evident,  therefore, 
that  here  is  a  disease  the  contagion  of  which  is  found  in 
the  sputum  and  also  in  the  breath  exhaled  when  cough- 
ing. The  ordinary  breath  does  not  contain  the  germs. 
^'IQ,  In  typhoid  fever  and  cholera  the  most  dis- 
•Vik  tinctive  characteristic  of  the  disease  is  the 
FIG.  72.  Ba-  diarrheal  discharges  from  the  alimentary  canal, 
cillus causing  and  this  suggests  that  the  faeces  may  be  the 
influenza  or  source  of  exit  of  infectious  material.  Thus, 
though  contagious  diseases  differ  very  much 
from  each  other,  it  is  rarely  difficult  to  determine  by 
observation  the  method  by  which  the  infectious  matter 
leaves  the  body  in  the  case  of  any  particular  contagious 
disease.  The  practical  fact  to  bear  in  mind  is  that  dur- 
ing the  progress  of  an  infectious  disease  any  unusual 
discharges  from  the  body,  mouth,  skin,  or  elsewhere  are 
almost  always  the  means  of  exit  of  the  parasites,  and  from 
such  excretions  all  members  of  a  household  should  be 
most  carefully  guarded.  Special  attention  should  be  given 
to  the  care  of  the  various  discharges  from  the  patient,  and 
if  this  is  done  the  contagion  may  be  reduced  very  largely, 
and  in  many  cases  be  absolutely  prevented. 

2.  How  Disease  Germs  are  carried  to  and  fro 

There  are  several  methods  by  which  infection  may 
be  carried  from  the  body  of  the  patient  to  that  of  the 
healthy  person.  In  the  case  of  some  diseases  it  is  chiefly 


HOW  DISEASE   GERMS   ARE   CARRIED          221 

by  direct  contact.  In  such  diseases  as  smallpox  or  scar- 
let fever,  where  the  infectious  material  is  probably  on  the 
skin,  contact  with  the  patient  would  be  very  likely  to 
infect  a  healthy  individual.  Hence,  with  all  diseases  of 
this  character,  isolation  is  rightly  considered  of  the  greatest 
importance  (see  page  241). 

With  most  diseases,  however,  other  means  of  transference 
are  more  common.  The  microorganisms  are  not  able  to 
travel  of  their  own  accord,  and  are  always  carried  about  by 
some  other  agencies,  the  chief  of  which  are  the  following. 

Insects.     Insects  are  occasionally  the  means  of  carrying 
infectious   material.     The    relation    of    the    mosquito    to 
malaria  has  been  mentioned,  and  flies  have  a          00 
very   close   relation    to    the   distribution   of 
typhoid   fever.     So   close   is  this  relation  that 

it    is    now    urged    that    the    name  typhoid  fly  FlG-  73-    Ba- 
cillus of  bu- 
should    be    used.     Fleas,  also,  distribute   the    bonicpiague. 

bubonic  plague,  which  has  recently  produced 
so  many  deaths  in  the  Old  World  (Fig.  73).  It  is  quite 
possible  that  insects  may  carry  the  infection  of  cholera 
and  some  other  diseases ;  but  we  know  little  upon  these 
matters  at  present.  We  are  thus  taught  to  avoid  flies,  to 
shun  mosquito  bites  and  flea  bites,  and,  in  short,  to  avoid 
insects  as  much  as  possible.  Mosquito  netting  has,  there- 
fore, an  actual  sanitary  value. 

Larger  Animals.  Occasionally  larger  animals  transmit 
infectious  microorganisms.  It  is  believed  that  diphtheria 
is  sometimes  carried  from  the  patient  in  the  sick  room  to 
another  person  by  cats  which  wander  about  the  house  at 
will.  The  bubonic  plague  which,  fortunately,  is  as  yet 
rare  in  this  country  but  which  is  producing  great  ravages 


222  BACTERIA,  YEASTS,  AND   MOLDS 

in  Europe,  Asia,  and  Africa,  is  known  to  be  transmitted  by 
rats.  Tuberculosis  is  sometimes  transmitted  by  cattle, 
through  their  milk,  to  children  drinking  it.  There  may 
be  other  instances  not  so  well  known  where  larger  animals 
are  the  means  of  distributing  infectious  material. 

Water.  The  distribution  of  disease  germs  by  means  of 
drinking  water  is  chiefly  confined  to  two  diseases,  typhoid 
fever  and  Asiatic  cholera.  Typhoid  fever  is  very  common 
and  many  epidemics  are  due  to  polluted  drinking  water. 
The  disease  is  caused  by  a  well-known  bacillus  (Fig.  74), 
and  the  method  by  which  the  water  becomes  contaminated 
is  very  easy  to  understand.  The  bacilli  live  in  the  intes- 
tines of  the  patient  and  are  carried  from  him  by  the 
excreta.  This  material  may  be  thrown 
upon  the  soil  or  into  earth  closets,  and  is 
liable  in  either  case  to  percolate  through 
the  soil  or  be  washed  by  rains  into  wells  or 

streams.     Wells  are  filled  with  water  that 
FIG.  74.     Bacillus 

of  typhoid  fever.  nas  soaked  through  the  soil,  and  are  quite 
readily  contaminated  with  typhoid  germs. 
Hence  well  water  has  been  a  very  common  source  of  the 
distribution  of  this  disease.  In  most  cities  the  excreta  are 
thrown  into  sewers  and  the  sewage  may  empty  later  into  a 
river.  Hence  the  drinking  water  of  cities  may  sometimes 
present  very  great  danger.  Cities  frequently  depend  upon 
the  water  of  running  streams,  and  nearly  all  streams  of  any 
size  in  civilized  communities  are  more  or  less  contaminated 
by  sewage  from  houses  or  towns  on  their  banks.  Such 
water  will  be  likely  occasionally  to  become  infected  with 
typhoid  bacilli ;  so  that  rivers  and  streams  are  positive 
sources  of  danger  to  communities  that  depend  upon  them 


WATER  AS  A  SOURCE   OF  DISEASE  223 

for  their  drinking  supplies.  The  result  of  drinking  such 
contaminated  water  is  the  development  of  many  cases  of 
typhoid  fever.  A  large  part  of  the  cases  of  this  disease  in 
cities  are  due  to  the  contamination  of  drinking  water.  Many 
epidemics  have  been  traced  to  just  such  a  source. 

The  Asiatic  cholera  bacillus  (Fig.  75)  has  also  in  recent 
years  been  shown  to  be  distributed  by  means  of  the  water 
supply.  The  practical  result  of  this  discovery  has  been 
that,  since  cities  have  learned  to  guard  their  water  sup- 
plies, severe  epidemics  of  cholera  have  been  prevented. 
This  subject,  however,  need  not  detain  us, 
as  the  disease  is  hardly  known  in  America. 
But  in  the  event  of  a  cholera  epidemic 
it  should  be  remembered  that  the  majority 
of  cases  are  due  to  drinking  water  that 

of  cholera. 

has  been  contaminated  with  cholera  bacilli. 

There  are  some  other  diseases  occasionally  distributed 
by  water,  but  they  are  rare  or  little  known.  We  need  not 
consider  them  in  our  discussion. 

The  practical  question  how  to  avoid  such  dangers  must 
face  the  head  of  every  household.  To  answer  this  we 
must  first  fully  realize  that  any  water  which  has  oppor- 
tunity for  sewage  contamination  is  dangerous  for  drink- 
ing, and  cities  supplied  only  with  water  directly  from 
rivers  or  streams  have  a  supply  that  is  frequently  unsafe 
for  use.  Those  cities,  however,  which  have  large  reser- 
voirs where  the  water  stands  for  some  time  will  have 
more  reliable  water,  since  the  standing  of  water  will  in 
time  always  purify  it  of  typhoid  bacilli.  The  danger  that 
the  water  supply  may  become  a  source  of  typhoid  fever  is, 
therefore,  confined  to  those  cities  that  use  the  water  of 


224  BACTERIA,   YEASTS,  AND   MOLDS 

running  streams,  or  those  that  pour  their  sewage  into  a  lake 
and  then  pump  the  water  out  for  drinking  purposes.  The 
housewife  in  the  city  cannot  control  her  water  supply. 
This  must  be  left  to  health  boards  and  water  commissions. 
But  she  should  learn  whether  the  water  is  from  a  source 
liable  to  be  contaminated  with  sewage.  If  so,  she  must 
regard  it  as  dangerous  and  bestir  herself  to  treat  it  in 
some  way  that  will  make  it  safe  for  drinking.  This  can 
be  easily  done  by  simply  boiling  the  water,  since  even  a 
brief  boiling  destroys  typhoid  bacteria.  This  is  the  only 
satisfactory  method  of  rendering  such  water  harmless. 
After  boiling,  the  water  may  be  cooled  with  ice  and  used 
for  drinking. 

Many  households  are  supplied  with  various  kinds  of  fil- 
ters attached  to  their  faucets  for  the  purpose  of  purifying 
the  water.  The  ordinary  filters  are  worse  than  useless. 
They  may  make  the  water  look  clear  and  may  remove 
some  of  the  solid  material ;  but,  while  it  looks  pure,  such 
water  is  no  safer  after  filtering  than  before.  Filters  in 
ordinary  use  have  no  value  whatsoever  in  removing  typhoid 
germs.  They  do  remove  large  particles  of  dirt,  but  bac- 
teria pass  through  them  as  easily  as  dust  through  mos- 
quito netting  ;  and  though  they  make  the  water  clear  they 
do  not  make  it  a  whit  less  dangerous. 

One  type  of  water  filter  (the  Pasteur,  the  Berkefeld,  and 
the  Chamberland)  is  able  to  remove  bacteria  from  water 
and  thus  remove  all  danger.  Such  a  filter  is  shown  -in 
Fig.  76.  The  actual  filter  is  a  cylinder  (Fig.  76,  a)  made 
of  unbaked  porcelain  which  is  placed  inside  of  a  metal 
covering.  The  water  enters  the  metal  tube  and  is  filtered 
through  into  the  inside  of  the  filter.  These  filters  have 


FILTERING   OF   DRINKING   WATER 


225 


been  in  use  for  several  years  and  are  quite  efficient  if  prop- 
erly cared  for.  But  in  the  ordinary  home  they  are  apt  to 
be  worse  than  useless,  since  bacteria  lodge  in  the  porcelain 
filter  and  grow  there,  so  that  the  water  passing  through 
will  be  actually  contaminated  in  filtering.  To  prevent 
this  requires  more  careful  attention 
than  will  generally  be  given  in  a 
house.  The  filtering  cylinder  should 
be  removed  every  day  and  carefully 
cleaned  by  a  thorough  brushing,  and 
about  every  fourth  day  it  should  be 
sterilized  by  boiling  in  water  for  five 
minutes.  This  kills  the  bacteria  in 
the  pores  of  the  filter  and  renders 
it  safe  for  a  few  days.  Unless  one 
is  willing  to  adopt  this  plan  of  regu- 
lar sterilization  of  the  filter,  it  is 
better  not  to  use  it  at  all.  There 
is  no  other  means  in  the  household 
of  filtering  water  which  will  remove 
from  it  the  danger  of  distributing 
typhoid  fever.  There  is  a  method 
by  which  the  water  supply  of  a 
whole  city  may  be  purified  by  filter- 
ing on  a  large  scale  ;  but  this  again 
must  be  left  to  the  public  officials, 

and  is  not  within  the  reach  of  the  housewife.     Her  sole 
method  of  purifying  suspicious  water  is  by  boiling. 

Aerated  Waters.  The  recognition  of  danger  connected 
with  ordinary  drinking  water  has  led  to  the  extension  of 
the  use  of  a  variety  of  aerated  waters,  Apollinaris  ivater, 


f 


FIG.  76.  Pasteur  filter, 
showing  the  filter  itself, 
a,  made  of  unbaked 
porcelain,  and  the  metal 
cover. 


226  BACTERIA,   YEASTS,   AND    MOLDS 

Seltzer  water,  etc.  Such  beverages  are  not  bacteria  free, 
and  a  study  of  a  large  variety  has  shown  that  occasion- 
ally the  number  of  bacteria  they  contain  is  considerable. 
Artificial  aeration,  that  is,  charging  the  water  with  carbon 
dioxide,  does  not  at  once  destroy  germs,  and  if  the  water 
thus  charged  contained  disease  germs  at  the  outset,  the 
water  is  not  rendered  any  safer  than  it  was  before  aera- 
tion. Such  artificially  prepared  waters,  therefore,  are, 
while  fresh,  no  safer  than  the  original  water  from  which 
they  are  made.  After  they  have  stood  for  a  few  weeks 
the  disease  germs  seem  to  die  and  the  water  becomes 
wholesome.  The  naturally  aerated  waters  are,  so  far  as 
known,  never  likely  to  be  impregnated  with  disease  germs. 
We  may  then  conclude  that  naturally  aerated  water  is  safe 
from  disease  bacteria,  and  that  other  forms  of  aerated 
water  are  practically  safe  if  they  are  not  too  fresh.  In 
general,  such  waters  are,  therefore,  more  reliable  than 
drinking  water  which  has  an  opportunity  for  sewage 
contamination. 

Ice.  The  question  has  been  raised  in  the  last  few  years 
whether  ice  made  from  sewage-contaminated  water  is  safe 
to  use  for  cooling  drinking  water.  Typhoid  bacilli  are  not 
killed  by  freezing,  and  it  has  been  claimed,  therefore,  that 
such  ice  is  as  dangerous  as  water.  A  more  careful  study 
of  the  subject  has  shown,  however,  that  although  the 
bacilli  are  not  killed  by  simple  freezing,  they  are  mostly 
rendered  harmless  if  they  remain  frozen  in  ice  for  several 
weeks.  Ice  harvested  in  the  winter  is  therefore  safe  to 
use  the  following  summer.  This  statement  applies  to 
clear  ice,  but  not  to  snow  ice  sometimes  found  on  the 
surface  of  frozen  ponds. 


MILK  AS   A  DISTRIBUTER   OF   DISEASE         227 

Milk.  Milk  is  a  means  of  distributing  certain  diseases  ; 
not,  indeed,  a  vehicle  by  which  a  contagious  disease  in  a 
household  is  carried  from  one  member  of  the  family  to 
another,  but  rather  a  source  by  which  diseases  from  out- 
side may  find  entrance  into  the  family.  The  diseases  com- 
monly attributable  to  milk  are  not  very  numerous,  four  of 
them  being  very  definite  and  one  of  a  somewhat  obscure 
type.  The  four  definite  diseases  are  tuberculosis,  diph- 
theria, scarlet  fever,  and  typhoid  fever.  The  other  one 
referred  to  is  the  indefinite  series  of  intestinal  troubles 
known  as  summer  complaint,  summer  diarrhea,  cholera 
infantnm,  etc.  These  are  all  characterized  by  the  pres- 
ence of  diarrhea,  and  are  particularly  common  in  warm 
weather. 

There  is  no  doubt  that  all  of  these  diseases  are  occa- 
sionally distributed  by  milk.  The  one  most  commonly 
attributed  to  this  source  is  typhoid  fever,  and  many 
instances  have  been  recorded  where  epidemics  of  typhoid 
have  been  due  directly  to  milk  contaminated  with  typhoid- 
fever  bacteria.  Epidemics  of  diphtheria  and  scarlet  fever 
have  also  been  traced  to  the  same  source,  though  more 
rarely.  The  question  whether  any  considerable  amount 
of  tuberculosis  is  attributable  to  milk  has  not  been 
settled  positively,  but  the  probability  seems  to  be  that 
milk  is  a  source  of  this  disease,  especially  for  young  chil- 
dren. Pure  milk,  however,  is  never  the  cause  of  any 
of  these  troubles.  Milk  fresh  from  a  healthy  cow  is 
never  the  source  of  any  of  the  diseases  above  mentioned, 
nor  indeed  do  any  of  them,  except  tuberculosis,  come 
directly  from  the  animal  producing  the  milk.  Some 
cows  have  tuberculosis  and  their  milk  may  be  dangerous ; 


228  BACTERIA,  YEASTS,  AND   MOLDS 

but  cows  probably  do  not  have  diphtheria,  typhoid,  or 
scarlet  fever.  Danger  from  these  diseases  lies  in  the  pos- 
sibility that  between  the  time  of  milking  and  the  time 
when  it  reaches  the  consumer  the  milk  may  have  been  con- 
taminated with  the  bacteria  which  produce  these  troubles, 
and  that  these  bacteria,  growing  in  the  milk,  may  render 
it  a  source  of  hidden  danger. 

The  relation  of  milk  bacteria  to  the  production  of 
summer  complaint  and  similar  diseases  is  not  so  well 
understood.  The  only  points  that  we  need  notice  are : 
(i)  Such  troubles  are  doubtless  due  to  the  bacteria  present 
in  the  milk.  (2)  They  are  consequently  much  more  likely 
to  be  associated  with  milk  in  summer  than  in  winter,  since 
bacteria  grow  much  faster  in  warm  than  in  cold  weather. 
(3)  Fresh  milk  which  has  been  kept  cool  is  less  liable  to 
produce  such  troubles  than  older  milk  which  has  been 
kept  warm,  partly,  no  doubt,  because  the  latter  contains 
more  bacteria  than  the  former.  Practically,  then,  the 
housewife  should  remember  that  old  milk  that  has  been 
kept  warm  is  a  source  of  danger,  and  that  occasionally 
even  fresh  milk  may  be  the  cause  of  the  diseases  above 
mentioned  unless  some  precautions  can  be  adopted. 

How  can  precautions  be  taken  in  the  household  against 
these  possible  dangers?  i.  We  notice  again  that  the  milk 
that  costs  the  most  is  the  best  and  most  reliable,  while 
the  cheapest  milk  is  not  only  the  poorest  food  but  also 
the  most  dangerous.  2.  Where  it  is  possible  to  obtain 
information  in  regard  to  the  character  of  the  source  of 
milk,  the  danger  of  contracting  disease  may  be  lessened. 
For  in  a  small  community  knowledge  concerning  the  man 
who  delivers  the  milk  should  enable  one  to  get  some  idea 


MILK  AS   A   DISTRIBUTER   OF   DISEASE         229 

as  to  whether  he  is  careful  or  careless  in  handling  it. 
In  general  it  is  well  not  to  buy  milk  from  a  dirty  or  care- 
less milkman,  for  such  a  man  is  much  more  likely  to  sell 
milk  that  is  a  source  of  danger.  For  this  reason  milk 
distributed  in  glass  bottles  is  more  reliable  than  that 
distributed  from  metal  cans.  3.  Practically  all  of  these 
dangers  may  be  avoided  by  the  use  of  pasteurized,  con- 
centrated, or  certified  milk.  The  latter  is  a  higher  grade 
of  milk,  coming  from  special  farms,  and  should  have  a 
certificate  from  a  medical  commission.  They  cost  more 
than  the  ordinary  grade,  but  are  safe  to  use,  and  may  be 
given  to  infants  without  fear  of  contagious  diseases.  In 
general,  then,  the  first  factor  to  be  considered  in  guard- 
ing the  family  from  disease  through  milk  is  the  obtaining 
of  the  supply  from  reliable  sources  only,  even  though  the 
price  may  be  higher.  This  will  give  a  more  reliable  prod- 
uct, one  that  is  more  valuable  as  a  food  and  less  liable  to 
produce  disease. 

But  in  many  households  this  may  not  be  possible,  and 
the  family  may  be  obliged  to  depend  upon  the  ordinary 
milk  supply  without  any  knowledge  of  its  source.  What 
should  be  done  under  these  circumstances?  Such  milk 
can  be  rendered  harmless,  so  far  as  concerns  the  diseases 
referred  to,  by  the  processes  of  sterilization  mentioned  on 
another  page.  Since  milk  from  an  unknown  source  may 
be  rendered  safe  for  use  in  this  way,  it  is  easy  to  under- 
stand why  sterilization  has  in  recent  years  come  to  be 
so  widely  adopted.  The  same  end  is  more  satisfactorily 
reached  by  pasteurization. 

Every  housekeeper  will  ask,  however,  whether  such  a 
precaution  is  necessary  under  ordinary  conditions.  This 


230  BACTERIA,   YEASTS,  AND    MOLDS 

general  question  cannot  be  answered  and  it  will  always  be  a 
matter  for  individual  decision.  That  there  is  some  danger 
is  certain.  Whether  the  danger  is  sufficient  to  warrant 
or  demand  the  pasteurization  of  all  ordinary  market  milk 
is  a  matter  of  opinion  upon  which  bacteriologists  are  not 
yet  agreed.  For  young  children  who  must  be  fed  upon 
cow's  milk  it  is,  under  the  conditions  of  modern  life, 
not  safe  to  use  the  ordinary  milk  supply.  Many  children 
are  brought  up  on  such  milk  without  suffering  materially 
therefrom  ;  but  if  it  is  used  with  young  children  there  is 
considerable  danger  of  the  diseases  mentioned,  especially 
diarrheal  troubles.  In  feeding  young  children,  therefore, 
it  is  wise,  and  almost  necessary,  to  adopt  some  method, 
preferably  pasteurization,  of  destroying  the  disease  germs 
that  may  be  present.  If  the  milk  is  to  be  used  by  adults, 
the  necessity  is  not  so  great,  for  adults  are  not  as  a  rule 
so  liable  to  diseases  from  this  source.  Nevertheless  milk 
from  the  common  milk  supply,  unless  pasteurized,  must 
be  looked  upon  as  a  possible  source  of  typhoid  fever  and 
some  other  troubles.  It  should  be  emphasized  especially 
that  milk  is  not  necessarily  harmless  because  it  has  not 
soured.  It  is  true  that  soured  milk  contains  more  bacteria 
than  sweet  milk,  but  most  of  them  are  harmless,  while  a 
sample  of  milk  that  is  perfectly  sweet  may  contain  disease 
bacteria  and  be  unsafe  to  use. 

The  Air.  The  readiness  with  which  bacteria  can  float 
in  the  air  suggests  that  they  may  be  easily  distributed  by 
this  means.  The  agency  of  air  in  distributing  diseases 
has  been  somewhat  overrated,  but  it  occurs  in  a  few  dis- 
eases which  we  usually  look  upon  as  extremely  contagious. 
Skin  diseases,  like  measles,  scarlet  fever,  and  smallpox,  are 


AIR  AS   A  DISTRIBUTER  OF   DISEASE          231 

distributed  by  the  air,  and  a  person  can  take  them  with- 
out coming  in  actual  contact  with  the  patient,  when  no 
other  means  of  infection  is  known  save  that  of  air  cur- 
rents. The  distribution  of  disease  bacteria  by  means  of 
air,  however,  does  not  extend  very  far  from  the  patient. 
If  bacteria  are  thrown  off  into  the  air,  a  second  person  in 
the  same  room  and  in  the  immediate  vicinity  may  become 
affected  by  them.  But  the  danger  is  confined  chiefly  to 
the  room  occupied  by  the  patient.  It  is  true  that  the 
germs  may  pass  into  other  rooms  or  out  of  doors,  but 
they  usually  cease  to  be  dangerous,  partly  because  they 
become  mixed  with  such  large  amounts  of  pure  air,  and 
partly  because  they  soon  settle  to  the  floor  or  ground 
and  are  destroyed  by  sunlight.  The  danger  of  taking 
such  diseases  decreases  rapidly  as  we  pass  from  the 
immediate  vicinity  of  the  patient.  The  danger  may  be 
much  decreased  if  the  skin  of  the  patient  be  kept  moist 
by  a  mixture  of  glycerine  and  water,  or  by  a  little  oil 
rubbed  on  the  skin.  This  may  be  done  in  scarlet  fever, 
during  the  later  stage,  when  the  skin  is  peeling,  and  the 
danger  of  contagion  will  thereby  be  lessened. 

From  these  facts  we  can  conceive  that  the  dust  and 
dirt  collecting  on  the  floor  of  the  sick  room  will  be  likely 
to  become  a  source  of  trouble.  The  dust  that  accumu- 
lates on  the  floors,  walls,  or  ceilings,  on  the  window  sills  or 
the  doors,  or  on  any  article  of  furniture  in  the  room  occu- 
pied by  a  patient,  is  likely  to  contain  the  living  disease 
bacteria.  Such  material  is  therefore  a  source  of  con- 
tagion, and  in  protecting  a  family  from  attacks  of  conta- 
gious diseases  the  dust  accumulations  of  the  sick  room 
must  be  looked  upon  as  a  special  source  of  danger. 


232  BACTERIA,  YEASTS,  AND    MOLDS 

In  a  few  diseases  characterized  by  coughing  the  germs  are 
distributed  by  air  from  the  mouths  of  the  patients.  The 
most  noticeable  of  these  are  consumption  (Fig.  77),  whoop- 
ing cough,  and  very  likely  measles  at  certain  stages.  The 
air  coughed  from  the  mouth  in  these  cases  contains  small 
particles  of  moisture  which  float  around  for  some  time, 
and  these  particles  are  likely  to  be  laden  with  disease 
germs.  As  long  as  this  water  is  floating  the  air 'may  be 
dangerous  to  another  person  breathing  it.  In  these  cases 
also  the  danger  is  practically  confined  to  the  immediate 
vicinity  of  the  patients,  for  these  particles 
of  moisture  do  not  float  very  long  but  soon 
sink  to  the  ground  or  come  in  contact  with 
the  walls  of  the  room.  Danger  is  confined 
to  within  a  few  feet  of  the  patient,  a  dis- 
tance as  great  as  that  of  the  next  room 
FIG.  77.  Bacillus  ..  __  .  , 

of  tuberculosis.       being  usually  sufficient  to  free  the  air  from 

such  floating  microorganisms.  The  only 
way  to  avoid  such  dangers  is  to  insist  upon  plenty  of  fresh 
air  in  the  sick  room,  and  to  air  the  rest  of  the  house 
frequently  and  thoroughly. 

Tuberculosis  (Fig.  77),  or  consumption,  has  a  special 
source  of  danger  in  the  sputum  of  the  patient.  This 
material  is  filled  with  the  dangerous  bacilli.  As  long  as 
it  is  kept  moist  they  have  little  chance  of  distribution  ;  but 
if  the  sputum  is  voided  on  the  floor  or  where  it  can  dry, 
the  dried  material  will  blow  around  as  dust,  still  contain- 
ing active  bacilli.  The  sputum  of  consumptive  patients 
should  be  received  in  old  cloths  which  can  be  burned, 
thus  destroying  all  danger,  or  in  special  cups  which  can 
be  sterilized  by  disinfectants. 


DUST  OF  SCHOOLROOMS  233 

It  is  extremely  important,  also,  to  remember  the  sig- 
nificance of  dust  in  a  schoolroom.  A  schoolroom  with 
children  from  many  homes  is  likely  to  be  a  collecting 
place  of  disease  germs.  The  children  frequently  bring 
such  germs  to  the  schoolroom,  where  they  are  distrib- 
uted through  the  air,  float  around  for  a  while,  and  even- 
tually settle  on  the  floor.  If  they  remained  on  the  floor 
they  would  be  harmless,  but  every  time  the  room  is 
swept  or  dusted  the  germs  are  stirred  up  again.  Sweeping 
and  dusting  a  schoolroom  decidedly  increases  the  danger 
of  contagion.  If  feather  dusters  could  be  discarded  and 
brooms  also  dispensed  with,  their  places  being  taken  by 
damp  cloths,  the  amount  of  contagion  would  be  materially 
reduced.  If  the  floors,  window  sills,  desks,  and  tables 
were  wiped  each  day,  the  dust,  instead  of  being  scattered 
through  the  room,  would  be  collected  and  removed  by  the 
damp  cloth.  The  cloth  should  subsequently  be  rinsed  and 
occasionally  washed  in  hot  water.  Where  this  method 
has  been  adopted  the  results  have  been  surprising.  One 
school,  for  example,  with  over  four  hundred  pupils,  burned 
up  the  feather  dusters  and  used  damp  cloths  for  cleaning. 
During  the  following  year  there  was  not  a  single  case  of 
contagious  disease  among  the  scholars,  an  altogether  new 
experience  for  the  school.  The  same  general  facts  would 
apply  equally  well  to  the  household.  Brooms  and  dusters 
simply  distribute  germs  through  the  air,  and  should  be 
dispensed  with  as  far  as  possible.  Vacuum  cleaners  and 
damp  cloths  should,  where  possible,  take  the  place  of  brooms 
and  dusters.  Woodwork  should  always  be  cleaned  with  a 
damp  cloth  rather  than  by  dusting.  No  simple  rule  will 
be  more  useful  in  checking  the  distribution  of  contagious 


234  BACTERIA,   YEASTS,  AND   MOLDS 

diseases  than  that  of  discarding  the  old-fashioned  method 
of  dusting  and  replacing  the  same  with  the  more  sani- 
tary one  of  wiping.  It  is  much  better  to  have  bacteria  in 
the  carpets,  where  they  will  die  after  a  time,  than  to  have 
them  in  the  air  that  we  breathe. 

Uncooked  Food.  Some  of  the  foods  that  come  upon  our 
tables  without  cooking  may  be  the  means  of  distributing 
disease.  This  is  not,  however,  very  common,  and  is  men- 
tioned only  as  a  possibility.  If  fruit  has  a  chance  to 
become  contaminated  with  infectious  material  (such  as 
sewage,  or  sewage-infected  water,  or  consumptive  sputum), 
and  is  eaten  uncooked,  the  person  eating  it  is  in  danger 
of  contracting  disease.  The  chance,  however,  of  fruit 
becoming  contaminated  with  disease  germs  is  not  very 
great,  and  we  cannot  therefore  look  upon  it  as  a  very 
serious  source  of  danger  in  a  household.  Lettuce,  celery, 
or  radishes  grown  on  sewage  farms  have  a  chance  of 
contamination  from  typhoid  germs  in  the  sewage  used 
for  fertilizing  the  soil,  and  have  been  pointed  out  as  pos- 
sible dangers.  Troubles  from  these  sources  are,  however, 
rare  and  may  be  commonly  neglected,  but  in  times  of  epi- 
demics it  is  always  wise  to  guard  against  even  this  pos- 
sible source  of  danger  by  avoiding  the  consumption  of 
fruit  or  vegetables  that  have  in  any  way  whatever  been 
exposed  to  a  chance  of  contamination. 

Although  it  is  thus  seen  that  quite  a  number  of  our 
foods  are  sources  of  possible  danger,  it  is  not  wise  to  be 
too  fearful  over  the  matter.  The  fact  that  certain  dis- 
eases under  certain  conditions  are  caused  by  some  of  our 
commonly  consumed  foods  must  be  admitted ;  but  it 
must  also  be  remembered  that  the  chances  in  each  case 


MEANS    OF   BACTERIAL   INVASION  235 

are  small ;  that  our  fathers  and  grandfathers  have  con- 
sumed similar  foods  for  generations  and  have  suffered 
only  occasionally  therefrom.  It  is  therefore  wiser  not  to 
be  over  alarmed  or  to  make  life  burdensome  by  too  great 
precautions,  but  simply  to  use  such  care  as  may  seem 
feasible  and  possible  in  our  homes,  and  not  give  up  the 
use  of  any  desirable  food  because  we  know  that  it  may 
be  an  occasional  source  of  danger.  Some  people  have 
actually  given  up  the  use  of  butter  and  milk  because  it 
has  been  shown  that  they  contain  so  many  bacteria.  Such 
a  procedure  is  sheer  nonsense.  The  facts  here  outlined 
have  been  given,  not  for  the  purpose  of  inducing  people 
to  avoid  the  use  of  such  materials,  but  merely  to  suggest 
to  them  the  wisdom  of  adopting  possible  precautions 
against  consuming  contaminated  foods. 

3.  Means  of  Invasion 

A  matter  of  almost  equal  importance  in  considering  the 
distribution  of  disease  is  the  means  by  which  the  bacteria 
get  into  the  body.  Each  species  may  have  its  own  means 
of  entering,  and  frequently  each  can  find  entrance  in  only 
one  way.  If  it  should  get  in  by  other  means  it  would  pro- 
duce no  injury.  Some  species,  however  (tuberculosis),  pro- 
duce' trouble,  no  matter  how  or  where  they  enter.  If  we 
know  the  means  of  entrance  of  any  contagious  material, 
we  are  of  course  in  a  much  better  position  to  guard  our- 
selves against  it.  The  important  means  of  entrance  are 
as  follows. 

The  Skin.  Some  diseases  find  entrance  chiefly  through 
the  skin.  This  is  true  of  the  bacteria  which  cause  the 


236  BACTERIA,  YEASTS,  AND    MOLDS 

many  little  sores,  festers,  boils,  and  abscesses,  all  of  which 
are  commonly  due  to  bacteria  entering  through  the  skin 
(Fig-  78)-     These  bacteria  are  harmless  in  the 
stomach,  and,  indeed,  we  are  swallowing  them 
all  the  time.     The  mouth  contains  great  num- 
bers of  these  bacteria,  as  well  as  numerous 
other  species,  but  they  do  us  no  injury.     Skin 
diseases  like  ringworm,  favus,  etc.,  enter  in 
the  same  way.     This  is  likewise  the  case  with 
lockjaw  (Fig.  79),  erysipelas  (Fig.  78,  b),  and 
various    forms    of    blood    poisoning,   some  of 
which  are  of  comparatively  little  importance, 
while  others  may  be  serious  and  fatal.     It  is 
FIG.  78.  Vari-  possibly  also   true   of  measles,  scarlet  fever, 
ous  pat  ho-  and  smallpox,  although  in  these  latter  cases 
gemc   cocci.  we  nave  really  no  knowledge  of  the  matter. 

a,  pus  cocci; 

b  cocci  pro-       But   tnough   these  diseases  enter  through 
ducingpneu-  the  skin,  it  should  be  remembered  that  the 
monia;  c,  surface  of  the  body  is  commonly  quite  well 
protected  against  the  invasion  of  microorgan- 
isms.    We  have  already  seen  that  the  skin  of 
fruits,    if  uninjured,    protects   the  softer  portion   of  the 
interior  from  decay  to  a  considerable  extent,  and  that  the 
organisms  which  produce  decay  usually  enter 
through  bruises,  cracks,  or  cuts  in  the  skin. 
Precisely  the  same  thing  is  true,  probably  to 
an  even   greater  extent,  in  the   case  of  the       FlG  ?9 
human  body.     The  outer  layer  of  the  skin  is  a     Bacillus  of 
protection  which  the  bacteria  cannot  ordinarily       tetanus 
penetrate.     If  therefore  the  skin  is  unbroken  and  unin- 
jured, a  person  is  almost  perfectly  protected  against  the 


INVASION   THROUGH   THE   SKIN  237 

invasion  of  the  particular  kinds  of  bacteria  which  pass  in 
through  the  skin.  A  person  whose  skin  is  not  broken  can 
without  danger  handle  infectious  material  which  might  pro- 
duce fatal  results  were  the  skin  cut  or  bruised.  It  is,  how- 
ever, hardly  ever  the  case  that  a  person's  skin  is  unbroken 
over  his  entire  body.  Cuts,  bruises,  and  scratches  break 
the  skin,  and  through  such  openings  microorganisms  may 
find  entrance  into  the  body.  A  little  sliver  in  the  skin  is 
frequently  the  starting  point  of  a  fester,  a  boil,  or  an 
abscess,  or  even  of  a  severe  and  perhaps  fatal  case  of 
blood  poisoning.  So  small  a  thing  as  a  pin  prick  may 
sometimes  allow  entrance  to  mischievous  bacteria. 

The  conclusion  of  all  this  is  that  a  whole  skin  is  a 
protection  which  can  almost  absolutely  be  relied  upon ; 
but  a  more  important  lesson  is  that  any  break  in  the 
skin  should  be  more  or  less  carefully  protected.  The 
almost  surely  fatal  disease  lockjaw  (tetanus)  comes  from 
soil  bacteria  getting  into  the  body  through  the  skin,  and 
is  apt  to  occur  in  wounds  made  by  rusty  nails,  etc.,  which 
have  been  lying  a  long  time  on  the  earth  and  have  become 
contaminated  with  the  lockjaw  bacillus.  All  cuts  and 
bruises  should  be  carefully  washed  with  boiled,  i.e.  steril- 
ized, water.  The  fear  of  bacteria  explains  why  the  sur- 
geon endeavors  to  clean  the  surfaces  of  wounds  by  some 
disinfectant  which  will  prevent  the  growth  of  micro- 
organisms. Here,  too,  is  the  reason  for  protecting  from 
further  contamination  a  wound  thus  cleansed,  by  covering 
with  bandage  or  plaster.  All  of  these  devices  are  for  the 
purpose  of  protecting  the  body  from  the  entrance  of  bac- 
teria, and  make  it  possible  for  the  wound  to  heal  readily 
without  the  disturbance  which  would  be  produced  if 


238  BACTERIA,  YEASTS,  AND   MOLDS 

bacteria  got  into  the  wound.  Modern  surgery  is  based  on 
the  simple  plan  of  keeping  bacteria  out  of  wounds.  The 
frequent  efficacy  of  treating  wounds  by  such  crude  meth- 
ods as  covering  them  with  tobacco  juice  or  even  mud 
is  due  to  the  fact  that  these  act  as  mild  antiseptics  and 
protect  wound  surfaces  from  the  entrance  of  dangerous 
organisms. 

The  skin  should  therefore  be  carefully  guarded,  and  in 
all  cases  of  diseases  connected  with  the  skin,  a  list  of 
which  has  been  given  above,  special  care  should  be  taken 
that  no  part  of  the  body  which  is  cut  or  bruised  or 
scratched,  or  has  sores  upon  the  surface,  should  be 
allowed  to  come  in  contact  with  infectious  material.  If 
this  is  done,  the  danger  of  contagion  will  be  greatly 
reduced.  Though  a  person  with  whole  skin  may  safely 
handle  infectious  material,  no  matter  how  dangerous  it  is, 
one  whose  hands  contain  even  the  smallest  pin  scratch 
might  contract  contagion  and  suffer  illness'or  death  from 
such  procedure. 

The  Mouth.  Some  diseases  find  entrance  through  the 
mouth  by  means  of  the  food  or  drink  swallowed.  They 
are  chiefly  typhoid  fever,  tuberculosis,  diphtheria,  and  cholera, 
although  there  are  some  others.  It  is  manifest  that  not 
only  is  the  chance  of  contagion  through  the  mouth  less 
than  when  a  disease  is  borne  by  air  currents  and  enters 
through  the  skin,  but  it  is  more  easily  prevented.  The 
diseases  mentioned  are  not  usually  regarded  as  very  con- 
tagious, except  in  the  case  of  diphtheria,  where  the  contagion 
may  be  through  food  (milk)  or  air.  To  prevent  contagion 
from  most  of  these  diseases  it  is  only  necessary  to  guard 
all  that  enters  the  mouth,  keeping  it  free  from  infection. 


ENTRANCE  OF  BACTERIA  THROUGH  THE  MOUTH    239 

Food  served  hot  is  free  from  danger.  Food  and  liquids 
should  be  specially  guarded  from  contamination  in  the 
sick  room,  especially  in  cases  of  typhoid  fever.  The 
utensils  used  by  the  sick  patient  should  never  be  used  by 
other  inmates  of  the  house.  Those  who  have  anything  to 
do  with  nursing  the  patient  or  handling  soiled  bedding 
should  be  especially  careful  that  nothing  has  an  oppor- 
tunity of  getting  into  their  mouths.  Contagion  in  these 
diseases  may  be  carried  by  the  fingers ;  for  if  a  person 
touches  the  patient  he  is  likely  to  have  his  fingers  con- 
taminated with  infectious  material,  and  should  he  subse- 
quently place  his  fingers  in  his  mouth,  infection  would  be 
very  likely  to  follow.  If  one  guards  everything  that  goes 
into  the  mouth,  the  chance  of  infection  is  slight.  It  is  a 
significant  fact  that  in  cases  of  typhoid  and  cholera  —  the 
most  typical  diseases  of  this  sort  —  nurses  and  doctors 
rarely  take  the  disease  from  their  patients.  They  have 
learned  the  method  of  infection,  and  guard  themselves 
by  keeping  infectious  material  from  their  mouths. 

Breathing.  Some  diseases  undoubtedly  enter  the  body 
with  the  breath.  Fortunately  the  diseases  thus  contracted 
are  few.  Foremost  among  them  stands  tuberculosis. 
Diphtheria  is  probably  contracted  in  the  same  way,  and 
possibly  the  grippe,  whooping  cough,  and  measles,  although 
in  regard  to  the  last  two  we  know  almost  nothing.  There 
is  no  means  of  protecting  ourselves  against  this  method  of 
infection  except  to  keep  away  from  individuals  suffering 
from  the  diseases.  As  already  mentioned,  the  bacteria 
that  pass  into  the  air  fill  the  space  in  the  immediate 
vicinity  of  the  patient,  but  do  not  disseminate  themselves 
to  a  very  great  distance.  Hence  persons  in  the  immediate 


240       BACTERIA,  YEASTS,  AND  MOLDS 

vicinity  of  the  patient  are  exposed  to  the  disease  by 
breathing  the  air,  while  those  at  some  distance  are  but 
slightly  exposed,  and  those  at  a  greater  distance  not  at  all. 
The  danger  is  mostly  confined  to  the  room  in  which  the 
patient  is  kept,  and  hardly  extends  to  the  rest  of  the 
household.  The  only  protection  against  this  method  of 
invasion,  then,  is  to  avoid  the  immediate  vicinity  of  the 
patient,  and  to  keep  the  air  of  the  room  and  the  rest  of 
the  house  as  fresh  as  possible.  If  one  who  is  obliged  to 
breathe  such  air  will  take  the  opportunity  frequently  to 
breathe  fresh  air  out  of  doors,  his  danger  will  be  reduced. 


CHAPTER    XVI 
PRACTICAL   SUGGESTIONS 

From  the  facts  outlined  it  is  very  easy  to  draw  certain 
practical  suggestions  for  dealing  with  contagious  diseases. 

Isolation.  In  the  case  of  highly  contagious  skin  diseases, 
such  as  scarlet  fever,  measles,  smallpox,  etc.,  the  patient 
must  be  isolated  from  the  rest  of  the  household  as  com- 
pletely as  possible.  This  should  be  done  by  confining 
him  to  one  room  and  allowing  no  one  to  enter  except 
those  necessarily  engaged  in  caring  for  him. 

The  same  general  treatment  may  be  applied  in  diseases 
characterized  by  coughing,  like  whooping  cough  and  con- 
sumption. Diphtheria,  also,  though  not  distinctly  a  cough- 
ing disease,  is  distributed  by  breath  that  is  forcibly  exhaled 
by  the  patient,  and  the  seriousness  of  the  disease  makes 
it  necessary  to  adopt  isolation.  While  it  is  manifest  that 
the  only  means  of  absolutely  avoiding  contagion  from 
tuberculosis  and  whooping  cough  is  to  isolate  the  patient, 
it  is  also  clear  that  complete  isolation  of  a  sufferer  from 
whooping  cough  or  tuberculosis  is  rarely  possible  in  an 
ordinary  household.  Diphtheria  is  such  a  serious  disease, 
so  rapidly  fatal,  and  its  course  is  usually  so  brief,  that  com- 
plete isolation  is  not  only  feasible  but  necessary.  The 
other  two  diseases  last  so  long  that  isolation  is  generally 
very  burdensome,  difficult,  or  impossible.  It  is  well  to 
remember  that  in  such  diseases  periods  of  coughing  are 

241 


242  BACTERIA,   YEASTS,  AND    MOLDS 

the  times  when  there  is  most  chance  of  contagion,  and 
that  all  well  persons  should,  so  far  as  possible,  be  kept 
away  from  the  vicinity  of  these  patients  at  the  time  of 
coughing.  If  this  is  done  and  the  sputum  is  cared  for, 
the  chance  of  contagion  is  much  reduced. 

The  question  often  arises  how  long  the  isolation  should 
be  continued.  One  must  usually  depend  upon  the  physi- 
cian or  board  of  health  for  an  answer  to  this  question, 
since  the  period  of  isolation  varies  with  different  diseases. 
For  scarlet  fever  it  is  about  six  weeks  ;  for  whooping  cough 
it  is  certainly  as  long  ;  for  diphtheria  the  time  of  necessary 
isolation  is  very  variable,  and  our  health  boards  and  physi- 
cians have  not  yet  determined  how  long  an  isolation  is  neces- 
sary to  prevent  a  convalescent  patient  from  transmitting 
the  disease  to  other  children.  Upon  this  matter  nothing 
positive  can  be  said  at  the  present  time.  In  general,  the 
period  of  isolation  must  be  determined  for  each  disease 
by  the  advice  of  physician  or  board  of  health. 

Excreta.  In  the  case  of  diseases  located  in  the  alimen- 
tary canal,  and  distributed  by  excreta,  isolation  of  the 
patient  is  not  so  necessary,  but  everything  that  comes  in 
contact  with  the  discharges  from  the  alimentary  canal 
should  be  carefully  guarded.  This  will  include  not  only 
the  discharges  from  the  intestine  but  also  those  from 
the  mouth.  All  possible  precautions  should  be  taken  to 
prevent  any  such  material  from  being  distributed  through 
the  household.  Such  diseases  can  very  easily  be  confined 
to  the  patient  and  the  sick  room  if  care  be  taken  with 
the  excreta,  if  all  soiled  materials  coming  in  contact  with 
the  patient  be  properly  treated,  and  all  eating  utensils 
thoroughly  disinfected. 


TREATMENT   OF    INFECTED   ARTICLES          243 

Clothing  and  Bedding.  Any  articles  of  clothing  that 
come  in  contact  with  a  patient,  any  towels  or  cloths 
used  in  bathing  him,  are  very  likely  to  be  mediums  for 
the  distribution  of  disease.  If  it  is  a  skin  disease,  the 
clothing  is  sure  to  become  infected.  If  the  disease  bac- 
teria are  eliminated  through  the  sputum  or  the  excre- 
ment, it  is  almost  inevitable  that  the  clothing,  especially 
the  bedding,  will  be  contaminated  with  infectious  material. 
In  all  skin  diseases,  as  well  as  in  cases  of  typhoid,  diph- 
theria, tuberculosis,  and  indeed  most  contagious  diseases, 
clothing  and  bedding  are  sources  of  infection  and  must 
be  guarded  carefully.  The  clothing  and  bedding  should 
not  be  sent  to  the  general  laundry  but  washed  separately 
and  thoroughly  boiled.  Nothing  should  be  worn  in  the 
sick  room  by  nurse  or  patient  that  cannot  be  washed, 
and  all  unwashable  fabrics,  curtains,  carpets,  etc.,  should 
be  removed  from  the  room  where  there  is  a  contagious 
disease. 

Eating  Utensils,  etc.  The  eating  utensils  used  by  a 
patient,  or  indeed  anything  that  he  handles  or  uses  dur- 
ing his  sickness,  may  be  very  easily  contaminated  with 
the  infectious  material.  It  is  perfectly  evident  that  a 
diphtheria  patient  who  has  the  bacilli  in  his  mouth  will 
contaminate  the  spoons,  knives,  and  forks  which  he  uses 
with  the  bacteria  that  are  producing  the  trouble  in  his 
throat.  The  same  thing  would  be  true,  though  perhaps 
to  a  less  extent,  of  all  contagious  diseases,  for  a  patient 
cannot  handle  anything  without  danger  of  thus  infecting 
it.  Consequently  all  utensils  from  the  sick  room  and 
all  articles  handled  by  the  patient  must  be  looked  upon 
as  means  of  distributing  the  disease.  The  practice  of 


244  BACTERIA,  YEASTS,  AND   MOLDS 

taking  the  spoons,  knives,  cups,  and  plates  from  which 
the  patient  has  taken  his  meals,  and  carrying  them  into 
the  kitchen  to  be  washed  with  the  other  household  uten- 
sils for  subsequent  use  by  the  rest  of  the  family,  is  a  dan- 
gerous one  and  is  one  of  the  easiest  and  perhaps  most 
common  means  of  distributing  the  disease  from  the  sick 
room  to  the  rest  of  the  household.  Doubtless  many  times 
the  distribution  of  diseases  is  attributable  to  the  indiscrim- 
inate use  of  the  same  eating  utensils  by  the  family.  It 
is  easy  to  avoid  this  danger,  (i)  Allow  no  one  to  use  the 
eating  utensils  which  the  patient  has  during  his  sickness. 
(2)  After  his  recovery  put  them  into  boiling  water  and 
leave  them  for  several  minutes.  Do  not  wash  them 
with  the  eating  utensils  of  the  rest  of  the  household. 
Thorough  boiling  will  render  them  harmless,  and  there- 
fore even  a  knife  or  a  spoon  coming  from  the  sick  room 
should  be  placed  in  boiling  water  before  it  is  used  by  any 
other  person.  It  must  be  borne  in  mind  that  water  that 
is  simply  hot  is  not  sufficient  for  this  purpose.  The 
water  must  be  boiling,  and  it  is  better  if  the  articles  are 
placed  in  the  water  and  the  water  boiled  for  five  or  ten 
minutes  before  they  are  taken  out  to  be  used.  The  state- 
ments made  concerning  eating  utensils  apply  also  to  any 
articles  handled  by  the  patient. 

Books  used  by  children  recovering  from  diphtheria  or 
scarlet  fever  and  then  returned  to  a  public  library  may 
distribute  disease  through  a  community.  In  cities  where 
the  schools  furnish  supplies  children  should  be  cautioned 
against  putting  into  their  mouths  pencils,  etc.,  particularly 
those  belonging  to  other  children.  If  a  person  has  a  scalp 
disease,  like  ringworm,  he  should  not  be  allowed  to  use 


TREATMENT   OF   THE    SICK  ROOM  245 

combs  or  brushes  used  by  other  members  of  the  family, 
for  other  cases  of  the  disease  would  be  sure  to  follow. 

Nurses.  Those  who  nurse  the  patient  should  take 
special  care  in  a  number  of  directions.  They  should 
have  a  change  of  clothing  to  put  on  when  they  leave  the 
sick  room  to  mingle  with  the  rest  in  the  house ;  they 
should  wash  their  hands  frequently  with  some  disin- 
fectant to  be  mentioned  later,  especially  after  handling 
the  patient,  his  bedding  or  his  clothes.  They  should  be 
especially  careful  to  avoid  putting  their  fingers  into  their 
mouths,  for  in  many  diseases  this  is  a  common  means  of 
infection.  A  nurse  who  carefully  observes  these  precau- 
tions is  much  less  liable  to  infection  from  any  of  the 
diseases.  The  face  also  requires  frequent  washing.  The 
hair  is  a  particularly  good  lodging  place  for  bacteria,  and 
a  good  nurse  wears  a  cap  to  protect  her  head  in  cases  of 
contagious  diseases. 

Treatment  of  the  Sick  Room.  After  the  recovery  of 
the  patient  it  is  necessary  that  the  room  he  has  occupied 
should  be  thoroughly  disinfected  before  any  other  mem- 
bers of  the  household  are  allowed  to  enter  it.  The  method 
of  disinfection  will  be  found  in  another  place.  We  will 
here  only  emphasize  the  fact  that  in  order  to  prevent  the 
appearance  of  other  cases  of  the  disease  such  disinfection 
is  absolutely  necessary  before  the  room  is  occupied  by  other 
people. 

The  treatment  after  recovery  from  a  contagious  disease 
is  sometimes  difficult  to  determine.  So  far  as  concerns 
the  patient  himself,  the  proper  procedure  after  recovery 
is  to  bathe  himself  thoroughly  in  a  disinfectant  solution 
suitable  for  this  purpose,  the  disinfection  or  bathing 


246  BACTERIA,   YEASTS,  AND    MOLDS 

including  the  hair  as  well  as  the  rest  of  the  body.  The 
person  should  be  given  clean  clothes  that  have  not  only 
been  thoroughly  washed  but  disinfected  by  proper  means  ; 
after  which  there  is  no  danger  of  his  transmitting  the 
disease  to  others. 

Sewage.  Since  the  discharges  from  patients  find  their 
way  into  sewage,  this  material  is  extremely  dangerous, 
indeed  from  the  standpoint  of  human  health  one  of  the 
most  dangerous  of  all  substances.  Every  effort  should 
be  made  in  the  household  to  guard  against  it.  Par- 
ticular attention  should  be  given  to  keeping  the  drinking- 
water  supply  from  becoming  contaminated  with  sewage. 
In  cases  where  the  water  is  from  a  well  there  should  be 
especial  precautions  against  contamination  from  privies  or 
sewage.  The  health  of  the  family  depends  upon  having 
the  well  a  long  distance  from  sewage  and  privies. 

In  cities  the  sewage  empties  commonly  into  one  gen- 
eral system,  and  most  of  the  houses  are  connected  by  a 
series  of  underground  channels.  These  sewers  carry  the 
discharges  from  all  the  patients  in  the  city,  and  hence 
contain  the  dangerous  disease  germs.  Since  each  house 
is  connected  with  this  system  of  sewerage,  it  is  of  the 
greatest  importance  in  modern  cities  that  the  connections 
with  the  sewer  pipes  should  be  most  carefully  guarded. 
Proper  plumbing  does  this  satisfactorily,  but  it  is  neces- 
sary that  the  plumbing  should  be  thorough  and  that  it 
should  occasionally  be  inspected.  All  bowls,  sinks,  and 
closets  should  be  connected  with  the  sewer  by  traps. 
The  general  design  of  such  a  trap  is  shown  in  Fig.  80. 
Between  the  bowl  or  sink  and  the  sewer  is  a  bent  tube 
filled  with  water.  As  long  as  this  trap  is  thoroughly 


SEWAGE 


247 


filled  with  water  no  bacteria  and  no  gas  can  pass  from 
the  sewer  into  the  sink.  If  the  joints  of  the  sewer  pipes 
are  tight  and  the  traps  are  full  of  water,  there  is  no  dan- 
ger that  anything  from  the  sewage  can  come  into  the 
rooms.  The  traps,  however,  occasionally  get  emptied  of 
water,  and  then  gases  may  pass  up  from  the  sewers. 
Moreover,  the  insides  of  these 
traps  become  breeding  places 
for  certain  kinds  of  bacteria, 
though  rarely  disease  bacteria, 
and  may  in  time  become  full 
of  them.  It  is  therefore  de- 
sirable to  pour  some  kind  of 
disinfectant  occasionally  into 
the  bowls  and  sinks.  A  weak 
solution  of  carbolic  acid,  one 
part  to  twenty,  or  a  solution 
of  chloride  of  lime,  one  part 
to  twelve,  put  into  bowls  and  Fla  8a  Diagram  showing  the 

sinks  will   disinfect    the  traps.        principle  of  two  kinds  of  traps 
It  is  also  an  excellent  plan   to        separating   washbowls   from 

.,.  r  sewers. 

pour  boiling  water  frequently 

down  sinks,  bowls,  and  closets,  for  this  not  only  helps 

to  clean  but  helps  also  to  disinfect. 

A  worse  danger  to  a  household  are  leaky  sewer  pipes. 
If  these  are  poorly  laid,  the  contents  of  the  sewer 
may  ooze  out  into  the  cellar  or  soil  under  the  cellar 
and  become  a  source  of  considerable  danger.  Leaking 
sewer  pipes  in  a  house  are  a  serious  menace.  The 
evils  from  sewer  gas  have,  however,  been  overrated.  Sewer 
gas  itself  is  not  capable  of  producing  any  specific  disease. 


248       BACTERIA,  YEASTS,  AND  MOLDS 

If  it  is  constantly  escaping  into  a  house,  the  members  of 
the  family  may  perhaps  become  weakened  by  constantly 
breathing  such  gas,  and  may  be  more  liable  to  the  attack 
of  parasitic  diseases.  Such  persons  might  perhaps  have 
a  tendency  to  throat  troubles ;  but  there  is  no  evidence 
in  our  possession  that  sewer  gas  can  cause  any  particular 
disease.  The  diseases  are  caused  not  by  gases  but  by 
living  bacteria ;  and  while  sewer  gas  may  be  deleterious 
in  its  weakening  action  upon  individuals  breathing  it,  it 
can  never  produce  disease. 

Protection  following  Cure ;  Immunity.  The  recovery 
from  a  contagious  disease,  as  a  rule,  protects  the  indi- 
vidual more  or  less  perfectly  from  a  second  attack  of 
the  same  disease.  But  the  amount  of  protection  differs 
with  different  diseases.  After  recovery  from  some  of  our 
contagious  diseases,  like  scarlet  fever,  a  person  rarely 
has  a  second  attack  during  life.  With  other  diseases  a 
second  attack  is  more  likely  to  follow,  but  in  all  cases 
there  is  at  least  a  temporary  protection  following  the 
recovery.  In  other  words,  after  a  person  has  recovered 
from  a  contagious  disease  he  is  not,  at  least  for  some 
time,  liable  to  the  same  disease  again.  This  protection 
lasts  in  some  cases  for  many  years  and  perhaps  through 
life  (scarlet  fever) ;  in  other  cases  it  may  last  only  a  few 
years  (measles?);  in  some  cases  perhaps  only  a  few 
months  or  weeks  (diphtheria);  but  a  temporary  protec- 
tion is  always  gained.  The  reason  why  one  is  thus  pro- 
tected from  a  second  attack  scientists  have  not  yet  wholly 
explained. 

Vaccination.  A  word  must  be  given  in  regard  to  the 
method  of  protecting  the  body  against  smallpox  known 


VACCINATION  249 

as  vaccination.  This  method  has  been  in  use  over  a 
hundred  years,  but  there  is  a  vast  deal  of  misunderstand- 
ing in  regard  to  it.  The  fact  of  the  case  is  that 
vaccination  gives  to  the  individual  a  certain  amount  of 
protection  against  the  dreaded  and  frequently  fatal  dis- 
ease, the  protection  being  due  to  about  the  same  cause 
as  that  which  produces  the  immunity  following  recovery 
from  germ  diseases.  The  protection  is  not  an  absolute 
one,  since  vaccinated  persons  do  occasionally  take  the 
disease.  But  for  a  time  after  vaccination  one  is  almost 
surely  protected  against  smallpox.  How  long  this  protec- 
tion may  last  no  one  knows.  It  certainly  does  not  last 
forever,  and  if  one  wishes  to  remain  immune  it  is  neces- 
sary to  repeat  the  vaccination  occasionally.  For  a  year  or 
two  after  vaccination  the  protection  is  strong  and  nearly 
absolute.  But  after  a  couple  of  years  it  gradually  becomes 
reduced,  and  after  ten  or  fifteen  years  the  amount  of 
protection  afforded  is  very  slight.  The  proper  method, 
therefore,  of  guarding  against  smallpox  is  vaccination  in 
childhood,  followed  by  vaccination  some  years  later,  and 
perhaps  again  at  intervals  in  later  life.  Experience  has 
shown  over  and  over  again  that  proper  attention  to  vacci- 
nation will  check  smallpox  epidemics,  and  no  other  means 
has  hitherto  been  satisfactory. 

It  must  be  recognized,  however,  that  vaccination  is  not 
always  harmless.  In  the  vast  majority  of  cases  the  per- 
son suffers  nothing  except  a  very  trifling  inconvenience 
from  the  treatment.  In  extremely  rare  cases,  perhaps, 
more  serious  results  arise.  If  these  secondary  troubles 
do  occur,  they  are  usually  not  due  directly  to  the  vaccina- 
tion but  to  the  vaccination  wound  becoming  contaminated 


250       BACTERIA,  YEASTS,  AND  MOLDS 

with  bacteria.  It  is  therefore  necessary  to  protect  the 
wound  carefully  against  possible  contamination.  This  is 
done  by  the  physician  in  various  ways.  Although  there 
is  thus  some  danger  in  vaccination,  the  chances  of  trouble 
are  very  slight  indeed,  whereas  the  protection  afforded 
against  smallpox  is  so  great  as  to  lead  scientific  men 
and  physicians  to  recommend  its  use  unhesitatingly  as 
a  general  protection  against  this  extremely  violent  and 
frequently  fatal  disease. 

Modern  physicians  have  means  of  almost  perfectly 
protecting  the  members  of  the  household  from  the  con- 
tagion of  diphtheria  by  means  of  the  product  known  as 
diphtheria  antitoxin.  Where  a  family  is  unable  to  isolate 
a  patient  from  other  children,  an  injection  of  antitoxin  is 
almost  certain  to  prevent  the  distribution  of  the  disease. 
Its  use  is  being  adopted  very  widely  by  physicians,  and 
every  housewife  should  understand  that  it  is  a  precaution- 
ary measure  that  is  eminently  wise,  perfectly  safe,  and  the 
only  known  means  of  protecting  a  family  where  complete 
isolation  of  a  diphtheria  patient  is  impossible.  Many  phy- 
sicians, indeed,  adopt  it  as  a  precautionary  measure  in 
households  where  there  are  several  children,  even  though 
the  patient  is  isolated. 

PHYSICAL  VIGOR  A  PROTECTION  AGAINST  CONTAGION 

The  best  protection  against  contagion  is  robust  health- 
A  person  in  strong,  vigorous  health  is  much  less  liable  to 
yield  to  disease  than  one  less  robust.  Consequently  in 
the  attempt  to  protect  the  household  from  contagious 
diseases  special  emphasis  should  be  placed  upon  methods 


PHYSICAL  VIGOR   A   PROTECTION  251 

of  increasing  the  physical  vigor  of  its  members.  This  can 
be  done  by  wholesome  food,  by  exercise,  and  by  fresh  air. 
An  active  body  is  far  less  liable  to  disease  than  one  more 
or  less  passive,  and  vigorous  exercise  in  the  open  air, 
accompanied  by  plenty  of  wholesome  but  not  too  rich 
food,  will  be  the  most  thorough  safeguard  an  individual 
can  have  against  the  attack  of  some  infectious  diseases, 
especially  tuberculosis.  The  need  of  fresh  air  should  be 
emphasized,  perhaps,  more  than  any  other  point,  for  the 
air  in  houses,  for  reasons  already  indicated,  is  much  more 
liable  to  be  filled  with  infectious  material  than  the  out- 
door air,  and  a  person  who  constantly  remains  in  the 
house  is  much  more  liable  to  yield  to  contagion.  ,If, 
however,  he  is  careful  to  exercise  in  the  open  air,  he  will 
ward  off  attacks  to  which  otherwise  he  might  yield. 
This  applies  even  more  forcibly  to  the  air  of  our  sleeping 
rooms  than  to  that  of  our  living  rooms,  for  fresh  air  in 
the  sleeping  room  is  one  of  the  greatest  desiderata  in 
maintaining  good  health.  The  belief  that  night  air  is 
injurious  is  responsible  for  much  ill  health.  Sleeping  in 
close  rooms  without  sufficient  air  causes  a  general  lower- 
ing of  bodily  vigor.  Our  sleeping  rooms  should  have 
the  windows  open  even  in  cold  weather,  and,  provided 
there  be  mosquito  nettings  at  the  windows  to  keep  out 
insects,  there  is  absolutely  nothing  to  be  feared  in  night 
air.  While  vigorous  health  is  a  protection  against  some 
diseases  (tuberculosis),  it  is  far  less  efficient  against  others 
(smallpox). 

It  should  always  be  borne  in  mind  that  contagious 
diseases  are  real  things,  and  not  the  result  of  imagination. 
They  are  produced  in  our  bodies  by  the  growth  of  certain 


252  BACTERIA,    YEASTS,  AND    MOLDS 

microscopic  animals  and  plants  in  our  blood,  muscles,  or 
elsewhere.  They  cannot  be  warded  off  by  simply  disbe- 
lieving in  their  existence,  and  the  sooner  the  housewife 
learns  that  a  contagious  disease  is  due  to  distinct  living 
beings  which  are  transported  from  one  person  to  another 
and  live  as  parasites  in  the  patient,  the  sooner  will  she  be 
in  a  position  to  protect  her  family  from  the  spread  of 
contagion. 

GENERAL  CONCLUSIONS 

Each  type  of  infectious  disease  must  be  fought  in  its 
own  way.  The  so-called  children's  diseases  are  so  decidedly 
contagious  that  isolation  alone  is  capable  of  preventing 
their  distribution.  Of  the  adult  diseases,  however,  the 
most  serious  may  be  largely  checked  by  proper  means. 
Smallpox  must  be  fought  with  vaccination  and  isolation, 
diphtheria  by  antitoxin  and  isolation,  typhoid  fever  by 
a  guard  placed  over  the  water  and  the  milk  supplies, 
malaria  by  destroying  the  breeding  places  of  mosquitoes 
and  protecting  oneself  from  mosquito  bites. 

Of  all  diseases,  however,  tuberculosis  is  most  widespread 
and  demands  most  attention.  The  common  form  of  this 
disease  is  consumption,  but  the  bacteria  may  attack  other 
parts  of  the  body,  producing  other  diseases,  such  as  scrofula, 
hip  disease,  etc.  Consumption  must  be  guarded  against 
by  destroying  the  sputum  of  patients  and  avoiding  their 
breath  while  coughing,  and  in  any  form  of  the  disease 
that  produces  open  sores  the  discharges  from  the  sores 
must  be  carefully  destroyed.  In  spite  of  the  long-accepted 
belief,  consumption  is  not  hereditary  but  is  contagious. 
Its  spread  through  families  is  due  to  the  close  association 


GENERAL   SANITARY   RULES  253 

of  patients  with  the  other  members  of  the  family.  It  is 
a  disease  associated  with  small  rooms,  poor  ventilation, 
and  crowded  houses  where  the  healthy  members  of  the 
family  live  with  consumptive  patients  and  frequently  sleep 
with  them.  Under  such  conditions  contagion  is  almost 
sure,  and  the  disease  spreads  from  person  to  person  just 
as  decay  spreads  from  apple  to  apple  in  a  barrel.  More 
air,  more  light,  more  care  of  the  sputum  and  other  dis- 
charges, greater  attention  given  to  guarding  against  the 
coughing  of  the  patient,  as  for  example  inducing  him  to 
cough  into  cloths  that  can  be  burned,  —  these  are  the 
remedies  against  the  spread  of  the  contagion,  and  strict 
attention  to  these  facts  would  soon  convince  any  one  that 
the  disease  is  not  hereditary  but  due  to  infectious  matter 
disseminated  from  the  patient.  The  child  of  a  consump- 
tive mother  may  even  nurse  at  his  mother's  breast  with 
little  danger  of  contagion ;  but  sleeping  with  her  and 
breathing  her  breath  while  she  is  coughing  is  very  likely 
to  give  him  the  disease  and  lead  to  the  erroneous  belief 
that  he  inherited  it  from  his  mother. 


GENERAL  RULES 

There  are  a  few  simple  rules  whose  observance  will 
reduce  the  chances  of  contagion.  These  rules  should  be 
followed  by  all,  but  it  is  particularly  important  that  chil- 
dren in  every  household,  and  especially  children  in  schools, 
should  be  taught  their  significance.  The  most  important 
rules  are : 

Do  not  spit  on  the  floor. 

Do  not  put  the  fingers  in  the  mouth. 


254  BACTERIA,  YEASTS,    AND    MOLDS 

Do  not  wet  the  fingers  in  the  mouth  for  the  purpose 
of  turning  the  leaves  of  books,  especially  library  books, 
inasmuch  as  book  leaves  are  sometimes  the  lurking  places 
of  disease  bacteria. 

Do  not  put  pencils  in  the  mouth. 

Do  not  put  money  in  the  mouth.  This  is  extremely 
important,  because  money  is  liable  to  come  in  contact 
with  all  sorts  of  people  and  to  become  contaminated  with 
many  kinds  of  disease  bacteria. 

Do  not  put  into  the  mouth  anything  that  another  per- 
son has  had  in  his  mouth.  This  refers  to  gum,  apple 
cores,  candy,  whistles,  bean  blowers,  drinking  cups,  etc. 

Turn  the  face  aside  from  others  when  coughing.  This 
will  sometimes  prevent  contagion  passing  from  one  per- 
son to  another,  inasmuch  as  the  breath  in  coughing 
distributes  disease  germs. 

Be  always  particular  about  personal  cleanliness,  fre- 
quently washing  the  face  and  hands. 


CHAPTER    XVII 
DISINFECTION 

In  every  household  the  problem  of  disinfection  is  sure 
to  arise  in  connection  with  contagious  diseases,  and  it  is 
a  question  of  more  or  less  serious  import  according  to  the 
seriousness  of  the  disease  and  the  number  of  inmates  in 
the  house.  The  purpose  of  all  disinfection  is  to  prevent 
the  spread  of  contagious  diseases  from  one  person  to 
another.  Hence  it  is  desired  to  destroy  the  microorgan- 
isms which  cause  the  disease.  If  this  can  be  done  there 
will  be  no  chance  of  contagion,  but  until  it  is  done  there 
is  always  a  possibility  that  a  healthy  person  may  contract 
disease  by  coming  in  contact  with  the  germs. 

In  connection  with  the  treatment  of  infected  material 
two  terms  are  frequently  confused.  An  antiseptic  is  a 
material  or  a  treatment  which  checks  the  growth  of  bac- 
teria, though  it  does  not  necessarily  kill  them  all.  It 
may  prevent  their  development  without  destroying  their 
life.  The  term  germicide,  when  properly  used,  refers 
to  treatment  which  totally  destroys  all  microorganisms. 
The  agents  which  are  used  as  antiseptics  are  also 
commonly  capable  of  acting  as  germicides  if  they  are 
used  in  larger  quantities,  and,  on  the  other  hand,  germi- 
cidal  substances  may  be  only  antiseptic  if  used  in  small 
quantities. 

In  considering  the  question  of  disinfection  in  the 
household  there  are  always  two  important  questions  to 

255 


256  BACTERIA,  YEASTS,  AND    MOLDS 

be  considered :  (i)  What  disinfectants  are  capable  of 
destroying  the  bacteria  ?  (2)  How  can  these  agents  be 
most  practically  applied  ?  It  is  of  course  manifest  that 
not  all  germicides  can  be  used  under  all  conditions.  Vio- 
lent poisons,  like  corrosive  sublimate,  might  be  used  in 
some  cases,  while  it  would  be  out  of  the  question  to  use 
them  in  others.  The  question,  therefore,  of  the  appli- 
cation of  the  disinfectants  is  of  even  more  importance 
than  a  knowledge  of  these  antiseptics  themselves. 

DISINFECTING  AGENTS  —  PHYSICAL 

The  physical  agencies  which  destroy  microorganisms 
have  already  been  considered  in  previous  chapters,  and 
a  summary  only  is  here  needed.  They  are  briefly  the 
following  : 

Heat.  All  active  growing  forms  of  bacteria  are 
destroyed  by  moderate  heat.  A  temperature  of  140°, 
maintained  for  half  an  hour,  is  usually  capable  of  de- 
stroying them,  and  a  higher  temperature  quickly  kills 
them.  Spores,  however,  are  not  killed  by  a  temperature 
short  of  actual  boiling,  and  some  spores  are  killed  only 
by  prolonged  boiling.  Moist  heat  of  steam  is  more  effi- 
cacious than  dry  heat.  Bacteria  spores  may  withstand  a 
dry  heat  of  280°  for  some  hours,  but  they  cannot  with- 
stand a  moist  heat  of  steam  that  is  much  above  boiling. 

A  matter  of  practical  importance  is  the  recognition  of 
the  fact  that  most  of  our  contagious  diseases  are  caused 
by  microorganisms  that  do  not  produce  spores.  Conse- 
quently lower  temperatures  than  boiling  are  commonly 
sufficient  for  disinfection.  The  only  common  disease  that 


PHYSICAL   DISINFECTING  AGENTS  257 

is  known  to  produce  spores  is  lockjaw;  for  while  there  are 
some  other  disease  germs  which  do  produce  spores,  the  ordi- 
nary diseases  of  the  household  which  we  look  upon  as  con- 
tagious are  not,  so  far  as  we  know  to-day,  disseminated 
by  means  of  spores.  Hence  the  practical  conclusion  is 
that  for  all  of  the  common  household  diseases  a  moist  tem- 
perature of  150°  or  1 60°,  maintained  for  half  an  hour, 
is  sufficient  for  disinfection ;  but  it  must  always  be 
borne  in  mind  that  this  will  not  disinfect  spore-producing 
material. 

Sunlight.  Bacteria  cannot  stand  direct  sunlight  for  more 
than  a  few  hours  without  being  killed,  —  the  brighter 
the  light  the  more  efficacious  its  action.  While  sunlight 
is  thus  an  acceptable  germicide,  its  practical  value  is 
limited  because  it  has  little  power  of  penetration.  Thin 
materials,  like  sheets,  which  can  be  exposed  to  direct  sun- 
light, will  be  disinfected  in  the  course  of  a  few  hours,  but 
heavier  materials,  like  blankets,  will  be  disinfected  only 
on  their  surface.  Anything  on  which  the  sunlight  can 
shine  directly  may  easily  be  disinfected  by  this  means, 
but  in  dimly  lighted  rooms  light  is  of  little  value  as  a 
disinfectant.  Its  use  is  therefore  limited  to  such  articles 
as  can  be  removed  from  the  rooms  and  exposed  to  the 
sun's  rays. 

Cold.  Cold  is  almost  useless  as  a  disinfectant.  It 
delays  the  growth  of  bacteria  for  a  while,  but  does  not 
destroy  them.  We  have  already  seen  that  long-continued 
freezing  in  ice  will,  after  some  months,  destroy  typhoid 
bacilli,  but,  except  in  the  case  of  a  few  diseases,  like 
yellow  fever,  freezing  is  of  no  value  as  a  -disinfecting 
agent. 


258  BACTERIA,   YEASTS,  AND    MOLDS 

DISINFECTING  AGENTS  —  CHEMICAL 

The  most  common  methods  of  disinfection  employ 
certain  chemical  agents  known  to  have  the  power  of 
destroying  bacteria.  There  is  a  long  list  of  germicidal 
substances.  We  need  notice  only  those  few  agents  that 
are  in  common  use. 

Corrosive  Sublimate.  This  is  one  of  the  most  efficient 
germicides,  and  its  small  cost  has  given  it  wide  use.  The 
most  common  strength  for  using  it  in  ordinary  conditions 
is  one  part  of  sublimate  to  one  thousand  parts  of  water.  At 
this  strength  it  rapidly  kills  bacteria.  This  strength  may 
be  used  for  washing  floors  or  walls  of  infected  rooms.  It 
may  be  used  for  washing  the  hands  after  touching  infec- 
tious materials.  It  is  an  excellent  antiseptic,  but  there 
are  two  objections  to  it.  (i)  It  is  intensely  poisonous,  and 
the  greatest  care  must  be  exercised  in  handling  it,  to  pre- 
vent it  from  reaching  the  mouth.  (2)  It  has  a  strong  cor- 
rosive action  on  metals  and  cannot  be  used  on  anything 
made  of  iron  or  steel.  These  facts  limit  its  use,  but  never- 
theless it  is  one  of  the  best  and  most  widely  used  of  chem- 
ical disinfectants.  A  solution  of  proper  strength,  one  to 
one  thousand,  may  be  made  by  dissolving  one  quarter  of 
an  ounce  of  corrosive  sublimate  in  two  gallons  of  water. 
A  more  effective  solution  is  as  follows. 

Corrosive  sublimate     .     .     .     .15  grains  (i  gram) 

Common  salt 30  grains  (2  grams) 

Water        i  quart  (1000  grams) 

Carbolic  Acid.  This  material  has  been  used  longer  than 
any  other  disinfectant,  and  is  very  efficient,  though  less 
so  than  corrosive  sublimate.  It  is  commonly  used  in  a 


CHEMICAL  DISINFECTING  AGENTS  259 

proportion  of  about  one  part  acid  to  twenty  parts  water, 
although  sometimes  it  may  be  weaker  and  sometimes 
stronger.  A  solution  of  one  part  to  twenty  may  be  used 
for  washing  the  hands,  but  stronger  solutions  will  produce 
a  burning  of  the  skin.  It  may  be  employed  for  almost  any 
of  the  purposes  for  which  corrosive  sublimate  is  used,  but 
its  value  is  less  and  its  cost  is  considerably  greater.  One 
of  the  reasons  for  its  popularity  is  the  fact  that  it  pos- 
sesses a  distinct  odor,  and  people  who  do  not  properly 
understand  the  matter  of  disinfection  have  an  impression 
that  a  disinfectant  ought  to  have  a  strong  odor.  It  should 
be  understood  thoroughly  at  the  outset  that  deodorants 
are  not  disinfectants.  Substances  with  strong  smells  do  not 
ordinarily  have  any  value  as  disinfectants.  The  odor  of 
carbolic  acid  is  almost  without  value,  and  the  security 
which  people  feel  when  a  disinfected  room  is  filled  with 
carbolic  acid  fumes  is  wholly  misplaced.  To  disinfect 
the  air  requires  materials  of  a  different  nature,  and  car- 
bolic acid  is  not  more  useful  as  a  disinfectant  than  are 
many  other  antiseptics  that  emit  no  odor  at  all.  Corro- 
sive sublimate,  for  example,  is  very  much  more  effica- 
cious than  carbolic  acid,  although  it  is  totally  without 
odor.  It  may  frequently  be  desirable  in  a  sick  room  to 
have  a  deodorant  as  well  as  a  disinfectant ;  but  this  is  for 
comfort  rather  than  for  safety,  and  other  deodorants  can 
be  employed  which  are  equally  as  efficacious  as  carbolic 
acid.  The  burning  of  coffee  grains  in  a  room  will  usu- 
ally destroy  offensive  smells  and  serve  as  a  deodorant, 
although  it  is  valueless  as  a  disinfectant. 

Chloride  of  Lime.     This  is  one  of  the  cheapest  and  at 
the  same  time  one  of  the  best  disinfectants.     It  may  be 


260  BACTERIA,  YEASTS,  AND   MOLDS 

applied  dry  if  the  material  to  be  disinfected  contains  mois- 
ture, but  it  acts  only  in  the  presence  of  moisture  and  should 
usually  be  dissolved  in  water.  A  solution  of  one  part  to 
twenty-five  of  water  (one  pound  to  six  gallons)  is  proper  for 
use,  and  is  extremely  efficient  in  disinfecting  walls,  floors, 
furniture,  etc.  Its  efficacy  is  due  to  the  chlorine  gas  liber- 
ated from  it.  Common  slacked  lime,  which  is  occasionally 
used,  is  of  little  value  as  a  disinfectant. 

Sulphur.  The  fumes  of  burning  sulphur  have  been 
widely  employed  for  disinfecting  rooms,  partly  because  of 
its  efficacy  and  partly  because  of  ease  of  application.  The 
common  method  of  procedure  is  to  shut  up  in  a  room  the 
articles  to  be  disinfected,  tightly  closing  all  cracks  around 
doors,  windows,  keyholes,  etc.,  and  to  burn  a  quantity  of 
sulphur  in  the  room.  Sulphur  can  be  used  only  in  spaces 
that  can  be  tightly  closed,  and  this  of  course  materially 
limits  its  application.  It  has  the  disadvantage  of  not 
readily  destroying  bacteria  spores,  and  therefore  not  being 
absolutely  effective.  In  spite  of  this  fact  it  is  found  to 
be  of  great  practical  value,  and  has  been  very  widely  and 
successfully  used  by  boards  of  health. 

Formalin.  The  desirability  of  some  disinfectant  in  the 
form  of  a  gas  that  can  be  used  for  disinfecting  rooms,  etc., 
has  led  to  the  use  of  a  new  disinfectant  known  as  formalin. 
This  material,  as  purchased,  looks  like  water,  and  consists 
of  a  poisonous  gas  dissolved  in  water.  The  liquid  itself 
is  a  very  effective  germicide,  one  part  of  formalin  to  ten 
thousand  parts  of  water  being  sufficient  to  destroy  the  vital- 
ity of  bacteria.  Formalin  has  no  more  injurious  action 
upon  clothing  than  common  water  would  have.  Hence 
it  may  be  used  very  freely  in  disinfecting  any  material 


APPLICATION    OF   DISINFECTANTS  261 

that  can  be  soaked  in  water.  Its  general  use  for  washing 
is  hardly  practicable,  because  it  gives  off  a  gas  that  is  very 
injurious  to  the  eyes  and  must  be  carefully  handled.  In 
recent  years  it  has  come  to  be  used  extensively  by  health 
boards  for  disinfecting  rooms.  Formaldehyde  gas  is  liber- 
ated in  considerable  quantity  and  allowed  to  act  in  closed 
rooms  for  a  number  of  hours.  To  liberate  the  gas  in 
quantity  various  devices  have  been  adopted.  One  of  the 
simplest  means  is  burning  what  are  known  as  formalin 
candles,  which  can  be  lighted  and  left  to  burn  in  a  room, 
giving  out  quantities  of  formalin  gas.  Other  methods 
require  special  apparatus  in  the  form  of  lamps,  etc.,  and 
are  not  within  the  reach  of  the  ordinary  householder. 
The  efficacy  of  this  gas  in  disinfecting  has  been  ques- 
tioned. It  appears  to  be  about  as  efficient  as  sulphur, 
and  under  some  circumstances  more  so,  though  not  an 
absolute  germicide  in  every  case.  It  is  probably  the  best 
gas  disinfectant  known. 

APPLICATION  OF  DISINFECTANTS 

In  determining  the  application  of  disinfectants  two  ques- 
tions arise  :  (i)  Where  should  the  disinfectant  be  applied? 

(2)  What  is  the  proper  disinfectant  to  apply?     In  most 
problems  that  confront  the  household  there  is  little  diffi- 
culty  in   determining    the   place   where   the   disinfectant 
should  be  applied.     We  should  look  in  at  least  four  dif- 
ferent directions  :  (i)  the  excreta  and  all  discharges  from  the 
patient ;   (2)  the  person  of  the  patient  or  of  the  attendant ; 

(3)  clothing,  including  all  bedding,  wearing  apparel,  etc. ; 

(4)  the  sick  room  itself  while  occupied  and  after  it  is  vacated. 


262  BACTERIA,   YEASTS,  AND    MOLDS 

Excreta.  All  discharges  from  a  patient  suffering  from 
any  infectious  disease  should  be  disinfected  at  once,  since 
they  will  always  contain  infectious  microorganisms.  This 
would  apply  to  the  faeces,  and  all  discharges  from  the  mouth, 
as  well  as  from  sores  on  the  skin,  etc.  Such  discharges 
should  be  placed  in  a  solution  of  corrosive  sublimate,  one 
part  sublimate  to  five  hundred  parts  water,  or  of  chloride  of 
lime,  six  ounces  to  a  gallon.  The  quantity  of  the  disin- 
fectant should  be  large,  and  the  material  should  be  allowed 
to  soak  in  it  for  at  least  an  hour  before  it  is  thrown  into 
closet  or  sewer.  Such  treatment  effectually  destroys  its 
pathogenic  nature.  It  is  of  course  difficult  to  disinfect 
discharges  from  the  skin,  but  all  pus  that  exudes  from 
such  sores  should  be  collected  and  thoroughly  disinfected. 

The  Person.  The  disinfection  of  the  patient  during 
disease  is  rarely  possible,  and  all  that  need  be  here  stated 
is  that  the  skin  should  be  kept  clean  by  bathing  in  water 
to  which  has  been  added  a  little  glycerine.  The  disinfec- 
tion of  the  person  of  nurse  or  attendant,  however,  should 
be  most  carefully  attended  to  in  cases  of  serious  infectious 
diseases.  The  hands  in  particular  are  liable  to  become 
infected  with  the  pathogenic  germs,  because  they  are  used 
in  handling  the  patient  and  his  bedding.  They  should  be 
carefully  washed  in  soap  and  water,  special  attention  being 
given  to  brushing  the  finger  nails  and  removing  all  possible 
dirt  from  them.  Afterwards  it  is  well  to  put  the  hands 
for  a  moment  in  strong  alcohol,  then,  before  drying,  in 
a  corrosive-sublimate  solution,  one  part  sublimate  to  one 
thousand  parts  water.  After  this  the  hands  should  be 
washed  again  in  clean  water.  Other  parts  of  the  body 
should  also  be  washed,  although  no  part  needs  it  so  much 


DISINFECTION    OF   CLOTHING  AND    BEDDING      263 

as  the  hands.  The  hair  should  occasionally  be  washed 
in  the  same  way,  although,  as  already  stated,  the  nurse 
should  use  a  cap  to  protect  the  hair  from  infection  as  far 
as  possible.  These  disinfections  should  be  frequent  in 
cases  of  serious  contagious  diseases,  and  should  always 
be  attended  to  when  the  nurse  leaves  the  sick  room  to 
mingle  with  the  rest  of  the  family. 

Clothing,  Bedding,  etc.  These  articles  almost  always 
offer  difficult  problems.  The  following  general  directions 
are  all  that  can  be  given. 

1.  Burn  everything  which  is  not  of  very  great  value. 
This  is  the  most  thorough  method  of  disinfection,  and 
therefore    care    should    be    taken    to   use  old,   worthless 
articles   as   much    as    possible,   in    order   that   they  may 
subsequently  be  burned  without  too  great  loss. 

2.  All  of  the  articles  that  can  be  boiled  should  be  sub- 
jected to  a  vigorous  boiling  for  at  least  half  an  hour.    This 
is  sufficient  for  complete  disinfection.     It  will  apply  to  all 
forms  of  thin  clothing,  like  cotton,  and  may  be  used  for 
sheets,  pillow  cases,  etc. 

3.  Articles  too  heavy  for  boiling,  or  those  that  would 
be  ruined  by  boiling,  cannot  be  so  easily  treated.     Any- 
thing that  can  be  soaked  in  water  without  injury  can  be 
disinfected  by  soaking  it  for  three  or  four  hours  in  a  solu- 
tion containing  one  part  of  formalin  to  five  thousand  parts 
of  water.     This  is  extremely  cheap  as  well  as  easy  to  make, 
and   may  be   employed  for  blankets   and   other   articles 
capable  of  soaking  in  water  without  ruin.     The  blankets 
should  be  placed  in  a  tub,  the  tub  filled  with  water,  and 
formalin  added  in  the  proportion  mentioned  above,  or  even 
as  strong  as  one  quarter  of  a  pint  formalin  to  ten  gallons  of 


264  BACTERIA,   YEASTS,  AND    MOLDS 

water.  A  soaking  in  such  a  solution  will  be  a  thorough 
disinfection.  For  heavier  articles  like  mattresses  and 
comfortables,  which  cannot  be  soaked,  there  is  no  satis- 
factory method  of  disinfection.  If  there  are  at  hand  facili- 
ties for  steaming,  these  articles  may  be  disinfected ;  but 
this  is  never  possible  at  home,  and  can  only  be  done  by 
health  boards.  Mattresses  in  particular  are  difficult  to 
disinfect  and  cannot  be  rendered  perfectly  safe.  For  this 
reason  care  sho,uld  be  taken  that  only  mattresses  of  little 
value  are  used  in  contagious  diseases,  so  that  later  they  may 
be  destroyed.  They  may,  however,  be  protected  consider- 
ably by  covering  them  with  a  rubber  blanket,  which  will 
prevent  their  becoming  contaminated.  Carpets  and  heavy 
curtains  can  be  disinfected  satisfactorily  only  by  means  of 
superheated  steam,  and  this  is  rarely  possible  in  a  private 
house.  Care  should  be  taken,  therefore,  to  remove  such 
articles  from  a  room  in  which  there  is  any  contagious 
disease. 

TREATMENT  OF  THE  SICK  ROOM 

While  occupied.  A  room  in  which  there  is  a  case  of 
contagious  disease  is,  under  the  very  best  circumstances, 
a  source  of  danger  to  all  persons  within  the  house,  and  it 
must  be  most  carefully  guarded  to  protect  the  other  mem- 
bers of  the  family  from  danger.  The  treatment  of  the 
room  during  its  occupancy  and  after  its  vacation  must  be 
totally  different.  While  the  room  is  occupied  by  the 
patient  not  very  much  can  be  done  to  control  the  conta- 
gion. Plenty  of  fresh  air  should  be  insisted  upon,  and 
obtained  by  the  proper  opening  of  windows,  care  being 
taken,  of  course,  to  shield  the  patient  from  draughts.  If  the 


TREATMENT   OF   THE    SICK   ROOM  265 

room  is  occupied  for  some  time,  it  may  be  well  to  wash 
occasionally  all  surfaces  of  furniture,  floors,  window  sills, 
etc.,  with  corrosive  sublimate  solution  as  described  above. 
The  patient  himself,  in  case  of  skin  disease,  may  be  bathed 
and  his  skin  be  kept  moist  with  water  containing  a  little 
glycerine  or  with  vaseline.  This  will  materially  diminish 
the  chance  of  infectious  material  floating  from  his  skin 
around  the  room.  All  contaminated  cloths  should  be 
burned  immediately,  and  care  should  be  taken  that  no 
one  passes  from  the  sick  room  to  mingle  with  the  other 
members  of  the  family  until  he  has  changed  his  clothes. 

Care  after  Vacation.  After  the  room  is  vacated  by  the 
patient  it  is  necessary  to  disinfect  it  thoroughly  before 
using  it  again.  The  disinfection  of  such  a  room  is  a  matter 
of  some  difficulty  and  many  methods  have  been  adopted 
for  the  purpose.  One  that  is  perhaps  as  satisfactory  as 
any  is  as  follows. 

Carpets,  curtains,  bedding,  and  all  cloth  material  should 
be  removed  and  disinfected  as  above  mentioned.  All 
surfaces  in  the  room,  including  walls,  ceiling,  floor,  tables, 
chairs,  and  especially  cracks  around  mopboards  and  floor, 
should  be  washed  freely  with  the  corrosive  sublimate  solu- 
tion or  with  the  chloride  of  lime  solution. 

If  this  washing  is  thorough,  including  all  surfaces  in 
the  room,  the  room  will  be  well  disinfected ;  but  it  is 
wise  and  customary  to  complete  the  process  by  the  use 
of  some  gaseous  disinfectant.  One  occasionally  used  is  sul- 
phur fumes.  The  best  method  of  applying  it  is,  first,  to 
close  tightly  all  cracks  and  then  to  place  the  sulphur  in  a 
metal  dish  in  the  middle  of  the  room,  preferably  putting 
the  vessel  in  a  tub  containing  an  inch  or  two  of  water. 


266  BACTERIA,   YEASTS,  AND   MOLDS 

A  little  alcohol  is  poured  upon  the  sulphur,  which  is  then 
ignited  and  the  room  quickly  closed.  Five  pounds  of  sul- 
phur should  be  burned  for  every  thousand  feet  of  space, 
and  the  room  should  be  left  closed  for  twenty-four  hours. 
While  such  sulphur  fumes  are  not  a  perfect  disinfectant, 
in  practice  the  method  has  been  found  satisfactory. 

In  these  days  formalin  gas  is  being  used,  more  than 
sulphur.  The  method  of  obtaining  the  gas  is  either 
through  the  burning  of  formalin  candles  or  the  using  of 
one  of  the  machines  devised  for  producing  such  gas. 
These,  however,  are  always  handled  by  boards  of  health, 
and  details  of  their  use  need  not  be  given  here.  After 
the  use  of  the  gaseous  disinfectant  all  windows  should 
be  thrown  open  to  allow  a  free  access  of  air. 

Disinfection  by  gas  cannot  be  absolutely  relied  upon, 
and  there  are  always  possibilities  of  a  disease  reoccurring 
in  the  room  if  it  is  occupied  immediately.  It  is  therefore 
wise,  where  possible,  to  leave  the  room  unoccupied  for 
some  time  after  it  is  vacated  by  the  patient,  but  this  is 
not  absolutely  necessary.  It  should  perhaps  also  be  stated 
that  if  the  room  is  thoroughly  washed  with  a  disinfectant 
solution  and  thoroughly  aired,  the  use  of  the  gaseous  dis- 
infectant is  unnecessary;  and  if  the  gaseous  disinfectant 
is  thoroughly  applied,  the  washing  is  unnecessary ;  either 
one,  if  thorough,  is  sufficient.  But  the  chance  of  some 
slip  in  the  application  makes  it  wise  to  use  both  methods, 
at  least  in  the  case  of  serious  contagious  diseases.  Dis- 
infection should  always  follow  smallpox,  measles,  diph- 
theria, tuberculosis,  and  typhoid  fever,  and  it  is  wise  to 
adopt  it  in  cases  of  mumps,  whooping  cough,  and  the 
other  lighter  contagious  diseases. 


APPENDIX 


DIRECTIONS    FOR    LABORATORY    EXPERIMENTS 

Apparatus.  The  experiments  here  described  are  all  of  a  simple 
character.  Many  of  them  can  be  performed  without  any  special 
apparatus  ;  but  some  would  need,  in  addition  to  test  tubes,  flasks,  and 
other  simple  glassware  found  in  any 
laboratory,  a  few  pieces,  as  follows. 

1.  A  steam  sterilizer.     An  ordinary 
steamer  such    as  used  in   the  kitchen 
will  do.     A  better  form    is  shown  in 
Fig.  81. 

2.  A  hot-air  sterilizer.    The  best  form 
is  shown  in  Fig.  82.    Some  sort  of  sheet- 
iron  box  which  will  serve  the  purpose 
may  be  found  in   almost  all  chemical 
laboratories. 

3.  Petri  dishes.     These  are  double 
glass  dishes,   Fig.  83,  several  dozen  of 
which  should  be  at  hand. 

4.  Glass  pipettes  to  hold  i  cc. 

5.  A  few  fermentation  tubes,  shown 
in  Fig.  38. 

6.  Pieces    of    platinum   wire    fused 

into  glass  rods  are  convenient  for  transferring  bacteria. 

7.  To  carry  out  the  microscopic  studies  there  will  be  needed  a 
microscope  with  a  two-thirds  and  a  one-sixth  inch  objective.     A  higher 
power  is  desirable  though  not  necessary.     In  addition,  glass  slides 
and  cover  glasses  will  be  needed. 

The  apparatus  above  listed  (except  the  microscope)  costs  little, 
and  many  of  the  experiments  can  be  performed  with  even  simpler 

improvised  material. 

267 


FIG.  8 1.     Steam  sterilizing 
apparatus. 


268 


BACTERIA,  YEASTS,  AND   MOLDS 


Method  of  Experimenting.  The  order  in  which  the  experiments 
are  given  is  the  one  which  most  naturally  follows  the  subjects  treated 
in  the  body  of  the  text,  and  should  be  followed  as  closely  as  possible. 

Where  possible  each 
scholar  should  perform 
the  experiments,  but 
this  will  be  found  imprac- 
ticable in  most  cases.  In 
such  cases  the  experi- 
ment must  be  performed 
by  the  teacher  in  the 
presence  of  the  class. 

Most  experiments  with 
microorganisms  require 
two  or  three  days  for  the 
bacteria  to  grow,  and 
the  observations  must 
therefore  be  made  some 
time  after  the  prepara- 
tion is  made.  Hence  it 
is  especially  important 


FIG.  82.     Hot-air  sterilizing  apparatus. 


that  everything  should 
be  carefully  and  intel- 
ligibly labeled  and  that  the  scholars  understand  the  meaning  of  the 
labels.  When  the  teacher  performs  the  experiments  the  scholars 
should  see  the  preparation  as  well  as  the  final  results,  and  each 
scholar  should  make  careful  notes. 

Sterilizing.  •  All  glassware  must  be 
sterilized  before  it  is  used.  This  is  abso- 
lutely necessary  and  the  success  of  the 
experiments  will  depend  upon  it.  The 
glassware  should  be  first  washed  clean. 
Then  all  test  tubes,  flasks,  and  fermenta- 
tion tubes  should  be  tightly  plugged  with 
cotton,  as  shown  in  Figs.  38  and  64,  and  then  placed,  with  all 
other  glass  apparatus,  in  the  dry  sterilizer.  By  means  of  a  Bunsen 
flame  the  sterilizer  should  then  be  heated  to  a  temperature  of  about 


FIG.  83.     A  petri  dish  for 
plate  cultures. 


APPENDIX  269 

340°  (170°  C.)  and  kept  at  this  temperature  for  one  hour.  After  cool- 
ing they  are  ready  for  use.  In  the  following  experiments  it  will  be 
understood  that  all  glassware  should  be  sterilized  before  using. 

EXPERIMENTS  ILLUSTRATING  THE  MOLDS 

1.  Mold  on  Bread.     Place  several  slices  of  bread  under  a  bell  glass 
or  any  dish  that  will  protect  it  from  evaporation.     Battery  jars,  large 
beakers,  or  even  common  bowls  will  answer.     Moisten  the  bread  with 
water  and  put  aside  in  a  warm  place  (80°  to  95°).     After  two  or  three 
days  the  bread  will  usually  show  signs  of  white  mold.     Allow  the 
mold  to  grow  until  some  color  appears  and  then  determine,  if  possible, 
whether  there  are  more  than  one  species  of  mold  on  the  bread. 

2.  Molds  on  Different  Foods.     Under  separate  bell  glasses  place 
bits  of  cheese,  some  pieces  of  lemon,  and  a  bit  of  banana.     Each  of 
these  should  be  moist.     Cover  and  set  aside  as  in  the  last  experiment. 
Molds  will  grow  in  a  few  days,  but  probably  different  species  will  grow 
upon  the  different  materials.     Compare  the  molds  and  determine  how 
many  kinds  can  be  seen. 

3.  Experiment  to  show  the  Mycelium.      Place  a  little  fruit  juice, 
such  as  may  be  obtained  from  canned  fruit,  in  test  tubes  or  in  homeo- 
pathic vials,  and  drop  a  few  mold  spores  from  the  last  experiment,  or 
a  little  dust  from  the  floor,  upon  the  surface  of  the  liquid.     Set  aside 
to  grow,  and  notice  how  the  molds  spread  and  send  fine  threads  into 
the  liquid.     Later  notice  that  colored  masses  of  spores  grow  in  the 
air  upon  the  surface  but  not  in  the  liquid  below. 

4.  Spores.     After  the  molds  of   the    previous  experiments  have 
begun  to  produce  spores,  as  shown  by  the  appearance  of  some  color, 
remove  a  little  spore  material  from  the  surface  with  a  knife  blade  or 
a  platinum  wire  and  examine  under  a  microscope.     For  this  purpose 
a  compound  microscope  is  necessary,  since  the  spores  are  very  small. 

5.  Growth  of  Mold  from  Spores.     Moisten  a  bit  of  bread  and  trans- 
fer with  a  platinum  wire  a  little  bit  of  the  spore  mass  from  a  vigor- 
ously growing  mold  to  the  surface  of  the  bread.     Cover  with  a  bell 
glass  and  set  aside  for  growth.     Examine  every  day,  and  note  that 
molds  start  from  the  points  where  the  bread  was  inoculated  with  the 
mold  spores. 


270       BACTERIA,  YEASTS,  AND  MOLDS 

Preparation  of  Gelatin  Culture  Medium 

For  the  following  experiments  it  is  necessary  to  prepare  a  jelly 
upon  which  molds  will  grow.  A  satisfactory  jelly  for  this  purpose  is 
as  follows. 

To  100  grams  of  gelatin  add  900  cc.  of  water  and  about  5  grams 
of  Liebig's  Extract  of  Beef,  and  boil  for  half  an  hour.  While  still 
hot  filter  the  material  through  absorbent  cotton.  In  using  absorbent 
cotton  for  this  purpose  a  large  funnel  should  be  used  and  the  absorb' 
ent  cotton  placed  in  it.  The  liquid  gelatin  is  poured  into  the  cotton, 
and  it  will  run  through  readily,  coming  out  as  a  tolerably  clear  solu- 
tion. Some  of  the  filtered  jelly  is  to  be  placed  in  sterilized  flasks  and 
some  in  test  .tubes,  about  10  cc.  in  each.  Plug  the  flasks  and  test  tubes 
with  cotton,  and  steam  the  jelly  in  a  common  steamer  for  about  twenty- 
five  minutes.  The  jelly  is  to  be  cooled  and  put  aside  for  twenty-four 
hours.  At  the  end  of  that  time  it  should  again  be  placed  in  the 
steamer  and  steamed  for  half  an  hour.  Once  more  set  it  aside  for 
twenty-four  hours,  and  upon  the  third  day  steam  it  again  for  half  an 
hour  and  cool.  Material  thus  prepared  should  give  a  clear,  slightly 
brownish  jelly,  which,  if  properly  sterilized,  will  keep  indefinitely.  It 
should  be  acid  to  litmus  paper. 

If  the  teacher  does  not  care  to  go  to  the  trouble  of  making  the 
gelatin,  she  can  buy  it  of  dealers  in  bacteriological  supplies.  The 
gelatin  culture  medium  which  is  sold  by  such  dealers  is  slightly 
alkaline,  and  should  be  rendered  a  little  acid  by  adding  HC1  until 
the  mixture  will  just  turn  blue  litmus  paper  red.  Molds  require  an 
acid  medium,  though  bacteria  need  one  with  an  alkaline  reaction. 

6.  Mold  Spores  in  Dust.     Melt  the  gelatin  in  three  or  four  of  the 
test  tubes  prepared  as  above  described,  and  pour  it  from  each  into  a 
sterilized  petri  dish.     Replace  the  cover  upon  the  dish  and  allow  the 
gelatin  to  harden.     Sweep  a  little  dust  from  the  floor  and  scatter  over 
the  surface  of  the  gelatin  in  one  petri  dish.     Scrape  some  dust  from 
a  crack  in  the  floor  and  sow  on  another  dish.     In  the  same  way  sow 
dust  from  other  places  upon  the  gelatin.     Set  aside  until  the  molds 
begin  to  grow,  and  examine  the  mold  colonies. 

7.  Molds  in  a  Dust  Cloth.     Prepare  two  petri  dishes  of  hardened 
gelatin,  as  in  Experiment  6,  and,  after  removing  the  cover,  shake 


APPENDIX  271 

the  dust  from  a  dry  dust  cloth  over  one  of  them.  After  leaving  it 
thus  exposed  to  the  air  for  two  minutes  replace  the  cover.  Over  a 
second  dish  shake  a  damp  dust  cloth.  Set  both  aside  and  compare 
the  number  of  molds  that  grow  in  the  two  plates.  Has  the  dampness 
prevented  the  distribution  of  mold  spores  ? 

8.  Molds  in  the  Air.     Prepare  four  dishes  of  hardened  gelatin. 
Expose  two  of  them  to  the  air  of  an  ordinary  room  that  has  been 
quiet  for  some  hours,  for  example  a  schoolroom  before  the  school 
has  assembled,  by  leaving  the  cover  off  for  two  minutes  and  then 
replacing  it.     Expose  two  other  plates  for  the  same  length  of  time 
at  the  close  of  the  school  session  after  the  air  has  become  stirred  up. 
Another  pair  of  plates  may  be  advantageously  exposed  in  the  hall 
while  the  scholars  are  passing.     All  plates  should  be  exposed  for  the 
same  length  of  time,  carefully  labeled,  and  set  aside  at  the  ordinary 
room   temperature  for  growth.      Count  the  number  of   molds  that 
grow  in  each  plate.     A  few  bacteria  colonies  will  be  likely  to  appear 
on  some  of  the  plates,  but  these  can  easily  be  distinguished  from 
molds  since  they  do  not  have  the  fuzzy  appearance  due  to  the  mold 
mycelium. 

9.  Molds  in  the  Air.     Repeat  the  above  experiment,  using  moist 
bread  instead  of  the  petri  dishes  of  gelatin.     After  exposure,  place 
under  bell  glasses  and  set  aside  for  growth.     The  results  will  be 
essentially  the  same  as  in  the  last  experiment,  though  less  striking. 

10.  Growth  from  Spores.     Prepare  a  petri  dish  of  hardened  gela- 
tin.    With  a  platinum  wire  or  the  tip  of  a  knife  blade  remove  a  bit 
of  the  spore  mass  from  some  mold  obtained  in  a  previous  experiment, 
and  transfer  it  to  the  surface  of  the  gelatin.     Touch  the  gelatin  in 
this  way  in  several  places  and  then  cover  and  set  aside  for  growth. 
After  two  or  three  days  note  that  a  mold  colony  begins  to  grow  from 
each  spot  where  the  wire  touched,  indicating  that  spores  have  been 
transferred  to  the  jelly.     Allow  the  molds  to  grow  for  two  or  three 
days,  examining  them  each  day  with  a  microscope  or,  if  a  microscope 
is  not  at  hand,  with  a  hand  lens.     Note  the  extension  of  the  mycelium 
through  the  gelatin,  and  later  the  development  of  minute  tufts  of 
spores  on  the  surface.  -.    . 

11.  Germination  of  Spores.     Sow  mold  spores  upon  the  surface 
of  a  petri  dish  of  hardened  gelatin  as  follows.     Select  one  of  the 


272  BACTERIA,  YEASTS,  AND    MOLDS 

dishes  previously  inoculated  and  showing  mold  colonies  in  vigorous 
growth,  some  of  which  bear  spores.  Remove  the  cover,  invert  it 
over  a  second  dish  of  hardened  gelatin  and  gently  tap  the  dish  con- 
taining the  molds.  This  will  cause  the  spores  to  fall  in  a  shower  into 
the  second  dish.  Replace  the  cover  and  set  the  newly  inoculated 
dish  aside  for  growth.  After  one  day  examine  the  surface  with  a 
microscope  to  see  if  the  spores  have  begun  to  germinate.  Usually 
they  will  not  show  much  growth  before  two  days.  When  they  begin 
to  germinate  study  carefully  with  a  microscope.  This  may  be  best 
done  by  dropping  a  thin  cover  glass  upon  the  surface  of  the  gelatin 
and  then  studying  the  spores  with  a  high-power  objective  (£-inch). 
The  germinating  spores  will  show  threads  protruding  from  them,  as 
shown  in  Fig.  4,  p.  15.  Examine  daily  for  several  days.  After  about 
three  days  it  will  be  possible  to  see  the  fruiting  branches  beginning 
to  grow  from  the  ordinary  threads,  as  shown  in  Fig.  5,  p.  15.  This 
study  is  very  instructive,  but  cannot  of  course  be  made  without  a 
good  microscope. 

12.  Fruiting  of  Molds.     In  the  same  way  study  a  variety  of  molds. 
To  obtain  a  variety  is  usually  easy.     One  needs  only  to  expose  to  the 
ordinary  air  two  or  three  of  the  petri  dishes  and  several  species  of 
mold  spores  are  almost  sure  to  drop  in.     They  cannot  be  distinguished 
until  they  begin  to  develop  their  fruit,  when  they  can  readily  be  sep- 
arated by  a  low-power  microscope  or  a  hand  lens.     If  the  spores 
are  sown  on  gelatin,  as  above  described,  the  method  of  development 
of  the  fruit  may  be  studied.     Methods  of  producing  fruit  in  the  com- 
mon molds  are  shown  in  Figs.  10-17.    The  study  of  two  or  three  species 
is  sufficient,  although  the  larger  the  number  of  studies  the  better. 

13.  The  Effect  of  Drying.     Place  under  a  bell  glass  two  slices  of 
bread,  one  of  which  is  damp,  either  naturally  or  by  being  slightly 
moistened  with  water,  and  the  other  dried.     Leave  for  two  or  three 
days  and  notice  the  effect  of  drying  in  preventing  the  growth  of 
molds.     If  one  slice  remains  dry,  no  molds  will  grow  upon  it  though 
the  other  soon  becomes  covered. 

14.  The  Effect  of  Boiling  Temperature.     In  each  of  two  test  tubes 
of  gelatin  place  a  small  quantity  of  mold  spores.     Melt  the  gelatin  in 
the  tubes  at  as  low  a  heat  as  will  melt  it.     Pour  the  contents  of  one 
tube  into  a  petri  dish  and  cover  at  once.     Place  the  other  tube  in 


APPENDIX  273 

a  beaker  of  boiling  water  and  allow  the  water  to  boil  briskly  for  half 
an  hour,  after  which  the  gelatin  is  to  be  poured  into  a  petri  dish  and 
treated  like  that  in  the  first  tube.  Set  both  dishes  aside  for  mold 
growth,  and  examine  at  intervals  for  several  days,  noticing  whether 
molds  develop  in  both  dishes  or  only  in  the  first.  If  they  grow  in 
both,  note  the  relative  abundance  in  the  two  dishes. 

15.  Effect  of  Low  Temperatures.     Prepare  two  plates  of  hardened 
gelatin  and  sow  mold  spores  upon  the  surface  of  each.     Leave  one  in 
the  ordinary  room  temperature  and  place  the  other  in  an  ice  chest  or 
some  other  place  where  the  temperature  is  low.    Compare  day  by  day, 
and  determine  the  effect  of  low  temperatures  in  checking  or  stopping 
mold  growth.     Do  any  molds  grow  upon  the  dish  placed  in  the  ice 
chest? 

1 6.  Effect  of  Air  Currents.     Moisten  a  slice  of  bread  and  sow  mold 
spores  "upon  it,  or  allow  it  to  mold  spontaneously  under  a  bell  glass. 
After  it  shows  a  luxuriant  growth  of  mold  remove  the  bell  glass  and 
leave  it  exposed  to  the  currents  of  the  air.     Notice  how  the  growth 
of  the  mold  ceases  and  the  delicate  mycelium  flattens  down  close  to 
the  bread. 

17.  Molds  in  Cheese.     Obtain  a  bit  of  Roquefort  cheese.     Cut  it 
open  and  remove  a  bit  of  the  green  mass  in  the  middle  by  means  of 
a  knife  point  or  a  platinum  wire.     Sow  this  substance  upon  the  sur- 
face of  a  dish  of  hardened  gelatin  and  set  aside  for  growth.     After 
two  or  three  days  the  molds  will  begin  to  develop  and  may  be  studied 
with  a  microscope.     When  they  begin  to  produce  fruit  they  should, 
if  possible,  be  studied  sufficiently  to  determine   the  species.     This 
species  of  mold  is  figured  in  Chapter  II  and  should  be  easily  identified. 

18.  Decay  of  Fruit  (a).    Place  in  a  jar  a  number  of  apples  that  have 
been  bruised  or  cut,  packing  them  in  rather  tightly.     Scatter  in  the 
jar  some  spores  of  the  common  blue  mold  which  will  usually  be  found 
on  some  of  the  petri  dishes  already  prepared.     Close  the  jar  and  set 
aside.     Prepare  a  second  jar  with  some  whole  clean  apples  and  treat 
in  the  same  way.     Compare  the  two  jars  for  a  week  or  two  to  see  if 
decay  makes  its  appearance  in  either  or  in  both  of  the  jars.     Does 
bruising  hasten  the  decay  of  the  fruit? 

19.  Decay  of  Fruit  (£).     Make  a  cut  through  the  skin  of  an  apple 
with  a  knife  blade  that  has  been  previously  dipped  into  the  midst  of 


274  BACTERIA,   YEASTS,  AND   MOLDS 

a  mass  of  mold  spores,  preferably  the  common  blue  mold.  Put  the 
apple  aside  in  a  jar  and  examine  carefully  until  it  decays.  Note  that 
the  decay  begins  rather  quickly  and  starts  at  the  point  of  the  cut 
where  the  spores  were  inoculated. 

20.  Molds  in  Decaying  Fruit.     Obtain  some  thoroughly  decayed 
fruit,   several   different   kinds   if   possible.      Remove    a   bit  of   the 
decayed  material  with  a  knife  blade  and  plant  it  in  gelatin  in  a 
petri  dish.     Replace  the  cover  and  set  aside  until  the  molds  begin  to 
germinate.    Allow  them  to  grow  for  a  number  of  days  and  then  study 
with  a  microscope,  determining  if  possible  the  method  of  forming 
spores  and  comparing  them  with  the  figures  of  molds  given  in  the 
previous  pages.     Is  the  species  found  similar  to  any  described  in 
this  work? 

EXPERIMENTS  ILLUSTRATING  YEASTS 

21.  Fermentation  of  Molasses.     Into  a  common  test  tube  or  any 
glass  vial  place  a  solution  made  by  mixing  one  spoonful  of  molasses 
with  ten  spoonfuls  of  water.     Rub  up  a  little  compressed  yeast  in 
water  and  put  a  few  drops  into  the  tube  of  molasses  water.     Set  aside 
in  a  warm  place  and  let  it  stand  for  about  twenty-four  hours.     At  the 
end  of  this  time  a  vigorous  fermentation  will  be  seen.     The  liquid  will 
have  become  somewhat  cloudy,  numerous  bubbles  can  be  seen  rising 
through  it,   a  froth  forms  on  top,  and  a  mass  of   sediment    soon 
collects  at  the  bottom.     The  bubbles  are  the  carbon  dioxide  which 
is  escaping  into  the  air,  the  sediment  at  the  bottom  is  the  growing 
mass   of   yeast,   and  the    alcohol,  which    looks   just   like    water,    is 
dissolved  in  the  liquid  and  is  of  course  invisible. 

22.  Proof  of  the  Nature  of  the  Gas.     Prepare  two  tubes,  as  shown 
in  Fig.  31.     In  tube  a  place  molasses  and  water  inoculated  with  sev- 
eral drops  of  yeast,  as  in  the  last  experiment.     Put  the  cork  in  place 
and  insert  the  other  end  of  the  tube  into  a  second  tube  underneath 
the  surface  of  some  clear  limewater,  as  shown  in  Fig.  31.     Set  aside 
in  a  warm  place  until  vigorous  fermentation  occurs.    Note  the  bubbles 
of  gas  that  arise  from  the  fermenting  tube  and  bubble  up  through 
the  limewater.    The  limewater  soon  becomes  turbid,  showing  that  the 
gas  contains  carbon  dioxide  (CO2). 


APPENDIX  2/5 

23.  C02  produced  chemically.     In  test  tube  a  of  a  pair  of  tubes 
similar  to  those  used  in  the  last  experiment  place  a  little  cream  of 
tartar  in  water;  in  another  test  tube  dissolve  some  saleratus  in  water. 
Pour  the  saleratus  solution  into  test  tube  a,  close  at  once  with  a  cork, 
and  allow  the  gas  produced  to  pass  into  limewater  as  before. 

MICROSCOPIC  STUDY  OF  YEASTS 

24.  Resting  Stage.     Rub  a  bit  of  yeast  cake  in  a  little  water  so 
as  to  make  a  slightly  cloudy  solution.     Place  a  drop  of  the  solution 
upon  a  microscope  slide,  cover  with  a  cover  glass,  and  examine  first 
with  a  f-inch  objective.     Note  that  the  water  seems  to  be  filled  with 
very  minute  dots.     Study  with  a  higher  power  (|-inch   objective). 
Examine  the  yeast  cells,  noting  the  shape,  comparative  size,  and  the 
vacuoles  inside  of  the  cells,  as  shown  in  Fig.   32.     Are  the  cells 
attached  or  are  they  mostly  separate?     Hunt  for  small  buds  upon 
the  sides  of  the  larger  cells.    Proceed  in  the  same  way  with  a  little 
dried  yeast  cake  and  compare  the  yeast  cells  in  size  and  appearance 
with  those  of  compressed  yeast. 

25.  Growing  Yeast.     With  a  pipette  remove  a  drop  of  the  sedi- 
ment  from    growing   yeast  prepared  as  in  Experiment  21.     Place 
the  drop  on  a  slide,  cover  with  a  cover  glass,  and  study  as  in  the 
previous  case.     Remove  some  of  the  yeast  found  floating  on  the  sur- 
face, and  study  in  the  same  way.     Note  that  the  yeast  cells  are  in 
groups.     Make  a  sketch  of  several  groups,  showing  buds  of  various 
sizes.     Can  you  see  the  vacuoles  in  the  cells,  as  in  the  first  specimen  ? 
Note  any  other  differences  you  can  see  between  this  growing  yeast 
and  the  compressed  yeast  cake. 

26.  Staining  Yeast.     Place  a  drop  of  yeast  upon  a  slide  and  cover 
with  a  cover  glass.     Place  a  drop  of  stain  upon  the  slide  beside  the 
specimen.     (Almost  any  stain  will  do.     Eosin  dissolved  in  water  is 
satisfactory.)     With  a  bit  of  blotting  paper  applied  to  the  edge  of 
the  cover  glass  opposite  to  the  stain,  draw  the  water  out  so  as  to 
suck  the  stain  under  the  glass.     Allow  the  stain  to  remain  about  two 
minutes,  and  then  place  a  drop  of  clear  water  beside  the  cover  glass 
and  with  a  blotter  draw  this  under  until  it  washes  out  the  stain. 
Then  examine  the  specimen  and  determine  whether  the  yeast  cells 


2/6  BACTERIA,  YEASTS,  AND    MOLDS 

are  stained  red.     It  should  be  found  that  most  of  them  are  unstained, 
although  a  few  are  stained  deep  red. 

27.  Staining  Boiled  Yeast.     Put  some  yeast  in  a  test  tube  with 
some  water.     Heat  to  boiling  for  a  few  seconds  and  then  remove 
Some  of  the  yeast  with  a  pipette  and  stain  it  as  above  described. 
After  washing,  study  to  see  if  the  yeast  which  has  been  killed  by 
boiling  stains  better  than  the  living  yeast. 

28.  Effect  of  Boiling.     Prepare   two  test  tubes  of  molasses  and 
water  and  inoculate  both  with  a  drop  of  yeast.     Plug  with  cotton. 
Place  one  test  tube  in  water  and  boil  for  ten  minutes,  and  then  leave 
both  test  tubes  side  by  side  in  a  warm  place  for  two  days,  and  deter- 
mine whether  the  boiling  has  been  sufficient  to  kill  the  yeast. 

29.  Wild  Yeast.     Prepare   several    test   tubes  of   molasses    and 
water  as  described  and,  without  plugging  with  cotton,  leave  exposed 
in  various  places  for  two  or  three  days.     Determine  by  the  appear- 
ance of  bubbles  whether  fermentation  occurs.     If  any  change  takes 
place  in  the  liquids,  examine  with  a  microscope  to  determine  whether 
yeasts  have  found  entrance  from  the   air  or  whether  some  other 
microorganisms  are  growing  in   the  solution.      Commonly  bacteria 
will  be  found  more  abundantly  than  yeasts. 

30.  Fermentation  of  Cider.     Grind  up  a  few  apples  and  strain  the 
juice  from  the  same  by  squeezing  through  cheese  cloth.     Collect  the 
juice  in  test  tubes  and  allow  it  to  stand  for  a  few  days.     A  fermenta- 
tion soon  appears  and  the  juice  turns  into  cider.    Examine  the  sediment 
with  a  microscope  and  detect  the  presence  of  yeast.    Close  up  the  tube 
with  a  cotton  plug  and  leave  it  for  a  number  of  weeks,  determining 
whether  it  subsequently  becomes  acid  by  the  development  of  acetic  acid. 

31.  Fermentation  of  Grape  Juice.     Proceed  as  above,  using  grapes 
instead  of  apples.    The  juice  will  become  wine  if  fermentation  occurs 
properly. 

32.  Effect  of  Temperature.     Fill  three  test  tubes  with  molasses  and 
water  as  above  described  and   inoculate   each  with  three  drops  of 
yeast  in  water.     Place  one   tube  in  a  refrigerator,  a  second  in  a 
moderately  warm  temperature,  about  70°,  and  a  third  in  a  warmer 
place,  near  a  stove  or  radiator  (temperature  about  90°).     Compare 
the  three  at  the  end  of  three,  six,  and  twenty-four  hours,  and  note 
the  effect  of  temperature  upon  growth. 


APPENDIX  277 

33.  Effect  of  Light.     Prepare  two  tubes  in  the  same  way  and  set 
one   in   a  bright  light  and   the   other   in  a  dark  place.     This  may 
be  best  done  by  wrapping  the  tube  in  velvet  or  heavy  black  paper 
to  keep  out  the  light.     Keep  both  tubes  at  the  same  temperature 
and  determine  whether  light  has  any  effect  upon   the  rapidity  of 
growth. 

34.  Effect  of  Age  on  Yeast.     Obtain  an  old  sample  of  dried  yeast 
cake.     Prepare  two  tubes  of  molasses  and  water  and  inoculate  one 
with  a  small  quantity  of  the  old  yeast  cake  and  two  others  with  a 
similar  quantity  of  a  fresh  cake.     Set  aside  in  a  warm  place  and 
determine  in  which  the  fermentation  starts  sooner,  and  in  which  it  is 
the  more  vigorous.     Examine  with  a  microscope  after  fermentation 
begins,  to  see  if  either  contains  other  organisms  besides  yeast. 

35.  Comparative  Fermenting  Power.     Make   a  dilute  mixture  of 
flour  and  water.     Fill  three  fermentation  tubes  with  the  mixture,  as 
shown  in  Fig.  38.     Inoculate  one  with  compressed  yeast,  a  second 
with  dried  yeast  cake,  and  a  third  with  brewer's  yeast,  if  it  can  be 
obtained.     Set  all  three  aside   in  a  warm  place  for  one   day,  and 
determine  the  relative  fermenting  power  of  the  different  yeasts  by 
comparing  the  quantities  of  gas  that  collect  in  the  closed  tubes.. 

36.  Action  of  Yeast  on  Bread.     Mix  up  a  little  flour  and  water  to 
about  the  consistency  of  dough  for  bread  making,  and  divide  into 
three  lots.     Into  a  and  b  place  a  little  compressed  yeast.     This  may 
best"  be  done  by  dissolving  the  yeast  in  water  and  stirring  it  into  the 
dough  during  the  mixing,     a  and  b  are  then  to  be  placed  in  a  warm 
place  for  five  or  six  hours,  while  c,  without  the  yeast,  is  to  be  baked 
at  once.     After  a  and  b  have  risen  under  the  influence  of  the  yeast, 
bake  b  at  once  in  the  oven,  while  c  is  to  be  thoroughly  kneaded  and 
then  baked.     Compare  the  results  of  #,  b,  and  c,  noticing  the  differ- 
ence in  the  textures  of  the  bread. 

37.  Overraising.     Mix   another  lot  of  dough   with  yeast  in  the 
same  way  and  allow  it  to  rise  in  a  warm  place  for  twelve  hours  or 
more.     Test  with  litmus  paper  to  see  if  it  is  acid.     Bake  and  taste 
to  see  if  it  has  become  sour. 

38.  Bread  raised  by  Wild  Yeast.    Put  a  small  amount  of  salt  in  a 
little  milk  and  then  allow  it  to  stand  in  a  warm  place  until  a  froth 
appears.     Mix  it  with  flour  to  make  a  dough  and  set  aside  to  rise. 


2?8  BACTERIA,  YEASTS,  AND    MOLDS 

Does  the  dough  rise  as  rapidly  and  as  satisfactorily  as  when  yeast  is 
used?     Does  the  baked  dough  have  the  same  taste? 

39.  Kumiss.    Into  a  quart  of  milk  put  two  tablespoonfuls  of  com- 
mon sugar  and  add  about  one  sixteenth  of  a  compressed  yeast  cake. 
Put  in  a  warm  place  and  leave   for  twenty-four  hours.     Cool  and 
taste.     It  will  be  kumiss,  or  fermented  milk.     Is  it  sour? 

EXPERIMENTS  ILLUSTRATING  BACTERIA 

40.  Putrefaction.     Place  in  a  series  of    test   tubes,  with  a   little 
cold  water,  the  following :  (a)  a  bit  of  raw  meat ;  (b)  some  white  of 
egg ;  (c)  some  flour  ;  (d)  some  crushed  beans  ;  (e)  sugar  ;  (f)  starch  ; 
(g)  a  bit  of  melted  butter.     Set  all  of  these  tubes  in  a  warm  place 
for  two  or  three  days  and  determine  which  will  putrefy  and  which 
will  not. 

41.  Effect  of  Moisture.     Place  a  little  of  the  following  foods  in  test 
tubes:   (a)  dry  beans;   (b)  Indian  meal;  (c)  a  piece  of  dry  bread; 
(d)  graham  meal ;  (e)  flour;  (f)  common  crackers.     In  another  series 
of  test  tubes  place  the  same  materials  moistened  with  water.     Set 
all  aside  in  a  warm  place  and  notice  the  effect  of  water  in  bringing 
about  putrefaction. 

42.  Effect  of  Temperature.     Place  bits  of  meat  with  a  little  water 
in  three  test  tubes.     Put  the  first  tube  in  an  ice  chest,  the  second  in 
ordinary  room  temperature,  and  the  third  close  to  a  stove  or  radiator, 
where  the  temperature  is  high.     Notice  the  rapidity  of  putrefaction 
in  each  case. 

43.  Effect  of  Boiling.     Chop  finely  some  raw  beef  and  place  it  in 
water,  warming  slightly  but  not  heating  it  to  more  than  130°.     Divide 
into  two  parts,  place  each  in  a  test  tube,  setting  one  aside  without 
further  treatment,  but  bringing  the  other  to  a  brisk  boil  for  a  moment 
and  then  setting  beside  the  first.     At  the  end  of  twenty-four  hours 
examine  to  determine  if  putrefaction  has  occurred. 

44.  Effect  of   Freezing.     The    following   experiment  can  be  per- 
formed only  in  cold  weather.     Place  a  little  hay  in  water  and  heat  to 
a  lukewarm  temperature,  leaving  the  same  to  steep  for  half  an  hour. 
Filter  through  filter  paper   into  two  test  tubes.     Plug  with  cotton 
and  set  one  of  the  test  tubes  in  a  warm  place.     Put  the  other  out  of 


APPENDIX  279 

doors  where  the  liquid  will  freeze.  Allow  it  to  remain  frozen  for  a 
few  hours,  and  then  bring  it  back  into  a  warm  room,  leaving  it  there 
for  a  few  days  to  see  if  it  putrefies,  in  order  to  determine  whether 
freezing  destroys  the  life  of  the  bacteria  in  the  hay  infusion.  For 
this  experiment  it  will  be  better  to  use  a  metal  dish  instead  of  a  test 
tube,  since  freezing  might  break  the  test  tube. 

45.  Effect  of  Boiling  upon  Spores.     Put  some  hay  into  a  dish  and 
steep  with   warm  water   at  about  120°.     After  an   hour's   steeping 
filter  through  filter  paper  into  four  test  tubes,  filling  each  half  full, 
plugging  the  same  with  cotton,  and  labeling  them  a,  b,  c,  d.     Bring 
a  to  a  boil  for  five  minutes,  b  for  ten  minutes,  c  for  twenty,  and  leave 
d  without  boiling.     Set  aside  for  a  few  days  to  determine  whether 
the  material  in  all  cases  putrefies.     Does  the  hay  infusion  contain 
bacteria  spores  that  are  not  killed  by  boiling? 

46.  Action  of  Disinfectants.     Mix  the  white  of  an  egg  with  ten 
times  its  bulk  of  water  and  place  the  material  in  a  series  of  test  tubes, 
filling  each  about  one  third  full.     To  the  tubes  add  the  following 
disinfectants  :  (a)  no  addition ;  (b)  one  quarter  of  a  gram  of  salt ; 
(c)  one  gram  of  salt ;  (d)  one  gram  of  sugar  ;  (e)  five  grams  of 
sugar ;    (f)  two  drops   of  a  corrosive-sublimate   solution  (one  part 
sublimate  to  one  thousand  parts  water) ;  (g)  six  drops  of  corrosive- 
sublimate    solution ;    (h).  one   drop  of   formalin ;    (i)   two    drops  of 
formalin ;  (j)  three  drops  of  formalin  ;  (k)  one  eighth  of  a  gram  of 
borax  ;  (1)  one  fourth  of  a  gram  of  borax  ;  (m)  four  drops  of  carbolic- 
acid  solution  (one  part  acid  to  twenty  parts  water)  ;  (n)  ten  drops  of 
carbolic-acid  solution.     Set  all  test  tubes  in  a  warm  place  side  by  side 
and  examine  daily,  noticing  the  effect  of  the  various  ingredients  in 
preventing  decay,  and  noting  how  much  more  powerful  some  disin- 
fectants (corrosive  sublimate)  are  than  others  (carbolic  acid).     Num- 
bers h,  i,  j,  m,  and  n  should  be  closed  with  a  cork  to  prevent  the 
disinfectant  from  evaporating. 

47.  Vinegar.     Soak  a  bit.of  raw  meat  in  vinegar,  warming  it  some- 
what and  leaving  it  for  several  hours.     Remove   the   bit  of  meat, 
placing  it  in  a  test  tube  plugged  with  cotton,  and  leave  for  a  few 
days,  to  determine  whether  it  putrefies  or  whether  the  vinegar  acts 
as  a  disinfectant.    The  vinegar  will  prevent  putrefaction  if  enough 
is  used. 


280  BACTERIA,   YEASTS,  AND   MOLDS 


MICROSCOPIC  STUDY  OF  BACTERIA 

It  is  rarely  feasible  to  carry  on  any  extended  microscopic  study  of 
bacteria  with  ordinary  classes.  The  organisms  are  so  minute  that 
they  require  very  high  powers  and  expensive  microscopes,  and  are  so 
simple  that  the  scholar  can  learn  very  little  by  their  study.  A  brief 
examination  of  a  few  bacteria  may,  however,  be  useful.  If  desired  it 
can  be  done  as  follows. 

48.  Study  of  Living  Bacteria.     Obtain  a  bit  of  decaying  meat, 
decaying  egg,  or  some  other  proteid  material,  and  place  a  minute 
drop  of  it  upon  a  slide  in  a  drop  of  water;  cover  with  a  cover  glass 
and  study  with  the  highest  objective  obtainable.     A  TVinch  objective 
is  required  to  study  them,  but  a  ^-inch  will  usually  be    sufficient 
to  show  the  bacteria  as  minute  specks,  many  of  which  will  commonly 
be  seen  swimming  rapidly  under  the  field  of  the  microscope.     If 
decaying  material  from  different  sources  is  studied,  there  will  usually 
be  found  several  kinds  of  bacteria,  as  indicated  by  the  different  sizes 
and  shapes. 

49.  Staining  Bacteria.     To  make  a  more  careful  study  of  these 
organisms,  they  must  be  stained  in  order  that  they  may  be  more 
clearly  visible.     Staining  fluids  may  be  bought  or  a  convenient  one 
be  prepared  as  follows: 

ZiehVs  Carbol-Fuchsin 

Saturated  alcoholic  solution  of  fuchsin 5  cc. 

Five  per  cent,  solution  of  carbolic  acid 45  cc. 

To  stain  bacteria  place  a  very  small  drop  of  some  decaying  mixture 
upon  a  cover  glass  in  a  drop  of  clear  water.  Spread  it  over  the  cover 
glass  in  as  thin  a  layer  as  possible,  and  then  allow  it  to  dry  in  the  air. 
After  drying  take  the  cover  glass  in  a  pair  of  forceps  and  pass  it  rap- 
idly through  a  gas  flame  three  times.  This  is  \tofix  the  bacteria  upon 
the  slide.  Place  a  few  drops  of  the  staining  fluid  upon  the  bacteria 
on  the  cover  glass  and  allow  the  stain  to  remain  for  five  minutes. 
Then  wash  thoroughly  in  a  stream  of  running  water  and  place  the 
cover  glass  upon  a  slide  in  a  drop  of  water,  bacteria  side  down. 
Study  with  the  highest-power  objective.  The  bacteria  will  be  found 


APPENDIX  28l 

to  be  stained  brilliant  red.  It  is  instructive  to  examine  a  number  of 
decaying  fluids  in  this  way. 

50.  Bacteria  from  the  Teeth.  Scrape  a  little  tartar  from  the  teeth, 
spread  upon  a  cover  glass,  and  stain  in  a  similar  manner. 

Further  microscopic  study  of  bacteria  requires  higher-power  objec- 
tives and  more  apparatus  than  can  be  found  in  ordinary  schools. 

CULTURE  EXPERIMENTS  WITH  BACTERIA 

Nearly  all  experiments  in  bacteriology  involve  the  use  of  culture 
media  prepared  for  the  purpose.  Such  culture  media  may  be  made 
by  any  one  who  has  at  his  command  a  laboratory  with  proper  appa- 
ratus for  sterilizing.  If  a  teacher  does  not  have  facilities  for  making 
culture  media,  they  may  be  bought  from  the  dealers  in  bacteriological 
apparatus.  The  following  is  easy  to  prepare. 

Gelatin  Culture  Medium 
Mix  together  in  a  common  stew  pan  the  following: 

i  liter  of  water. 

5  grams  of  Liebig's  extract  of  beef. 
10  grams  of  peptone. 
100  grams  of  gelatin. 

Carefully  weigh  the  mixture  in  the  dish  in  which  it  is  to  be  boiled. 
Heat  the  mixture  at  about  140°  until  the  gelatin  is  thoroughly  melted, 
and  then  boil  briskly  for  a  few  moments.  Test  with  litmus  paper. 
It  will  be  found  to  be  acid.  Add  to  it,  drop  by  drop,  a  solution  of 
caustic  soda  (NaOH)  until  it  is  slightly  alkaline  to  litmus  paper. 
Boil  briskly  for  half  an  hour.  Weigh  once  more,  add  enough  water 
to  bring  it  up  to  the  original  weight,  and  test  again  with  litmus 
paper.  If  the  reaction  is  still  slightly  alkaline,  the  material  is  ready 
for  filtering.  Filter  through  absorbent  cotton,  as  already  described, 
and  collect  the  clear  liquid  in  a  sterilized  liter  flask.  Fill  with  the 
material  as  many  sterilized  test  tubes  as  it  is  desired  to  use,  putting 
about  10  cc.  in  each,  which  should  fill  them  about  two  inches  deep. 
Replace  the  plugs  and  then  steam  all  of  the  gelatin  in  a  steamer  for 


282  BACTERIA,   YEASTS,  AND    MOLDS 

about  half  an  hour.  Set  aside  for  twenty-four  hours,  and  steam 
again;  and  after  another  twenty-four  hours  steam  a  third  time.  If 
properly  made,  the  material  will  still  be  clear,  and,  being  now  sterile, 
will  remain  clear  indefinitely.  It  differs  from  the  medium  prepared 
for  molds  chiefly  in  being  alkaline  instead  of  acid. 

Agar  Culture  Medium 

For  some  purposes  a  modification  of  the  above  is  desirable.  It  is 
made  in  the  same  way,  except  that,  instead  of  using  100  grams  of 
gelatin,  there  are  placed  in  the  mixture  i  .8  grams  of  agar-agar  (a  prep- 
aration from  a  sea  moss  which  may  be  purchased  from  dealers).  This 
is  known  as  agar  culture  medium.  In  other  respects  it  is  made  pre- 
cisely as  above,  except  that  more  heat  is  required  to  melt  agar  than 
to  melt  gelatin. 

51.  Bacteria  in  Tap  Water.     Melt  six  of  the  gelatin  tubes  by  mod- 
erate heat.    By  means  of  a  sterilized  pipette,  preferably  one  that  holds 
exactly  one  cubic  centimeter,  place  in  each  of  the  six  tubes  a  cubic 
centimeter  of  water  drawn  directly  from  the  tap.     Mix  the  water  thor- 
oughly with  the  gelatin  and  pour  the  contents  of  each  tube  into  a 
petri  dish,  covering  it  at  once  and  allowing  it  to  cool.     Set  aside 
at  a  temperature  not  above  70°.     In  about  two  days  the  dishes  will 
be  found  to  be  covered  with  little  dots  known  as  colonies.     These 
will  be  somewhat  variable  in  appearance,  but  since  each  colony  repre- 
sents what  was  a  single  bacterium  in  the  original  drop  of  water,  the 
counting  of  these  colonies  in  the  plate  will  give  the  number  of  bac- 
teria in  the  tap  water. 

52.  Bacteria  in  Well  Water.     Proceed  in  the  same  way  with  the 
water  drawn  from  a  well  if  it  is  obtainable. 

53.  Bacteria  in  Miscellaneous  Waters.     Obtain  samples  cf  water 
in  sterilized  bottles  from  several  sources  —  horse  troughs,  gutters,  run- 
ning water  of  the  streets,  snow,  etc.  —  and  treat  them  in  the  same  way 
as  described  above.     Comparison  of  the  plates  will  give  an  idea  of 
the  relative  number  of  bacteria  in  water  from  different  sources. 

54.  Bacteria  in  Ice.     Obtain  a  piece  of  ice  and  melt  it  in  a  steril- 
ized beaker.     Place  a  cubic  centimeter  of  the  water  in  gelatin  and 
proceed  as  above  described. 


APPENDIX  283 

55.  Bacteria  from  Various  Sources,     (a)  Into  three  tubes  of  melted 
gelatin  culture  medium  place  a  small  drop  of  saliva.     Mix  thoroughly 
with  the  gelatin  and  pour  into  petri  dishes.     (<£)  Place  in  other  tubes 
of  melted  gelatin,  and  also  of  melted  agar,  very  small  bits  of  decaying 
meat  or  decaying  egg.     Mix  thoroughly  in  the  gelatin  by  rubbing 
with  a  sterilized  glass  rod  and  pour  out  into  a  petri  dish.     (V)  Into  a 
third  set  of  tubes  place  small  pieces  of  dirt  swept  up  from  the  floor 
or  picked  out  of  cracks  in  the  floor.     Mix  with  the  gelatin  and  pour 
into  petri  dishes.     (W)  Into  a  fourth  set  of  tubes  place  a  little  dirt  from 
the  street  and  proceed  as  before.     Allow  all  plates  to  grow  till  the 
colonies  are  visible.     Note  any  differences  between  them. 

56.  Bacteria  on  the  Fingers.     Pour  gelatin  into  some  petri  dishes. 
After  it  has  hardened  touch  its  surface  with  the  fingers,  replace  the 
cover,  and  set  aside  for  bacterial  growth.    Wash  the  hands  thoroughly 
in  clean  water,  wiping  with  a  clean  towel,  and  then  proceed  in  the 
same  way  with  a  second  petri  dish,  touching  the  surface  with  the 
fingers  and  setting  aside  for  growth. 

57.  Bacteria  in  the  Air.     Melt  the  contents  of  four  tubes  of  gelatin 
and  four  of  agar.     Pour  each  into  a  petri  dish,  replace  the  cover,  and 
allow  the  contents  to  harden  without  inoculation.     Expose  one  gelatin 
and  one  agar  plate  to  the  air  of  a  schoolroom  before  the  school  ses- 
sion, by  removing  the  covers  and  leaving  the  plates  uncovered  for  three 
minutes.     Expose  two  similar  plates  at  the  close  of  the  school  session 
in  the  same  way.     Expose  two  in  the  hall  at  the  time  when  many  schol- 
ars are  passing  through  it.     Expose  two  in  a  room  after  sweeping  or 
dusting.     In  all  cases  the  plates  are  to  be  exposed  the  same  length  of 
time,  carefully  labeled,  and  set  aside  for  the  bacteria  to  grow.     The 
relative  number  of  bacteria  is  readily  determined  by  an  examination  of 
the  plates.     Molds  will  grow  upon  the  surface  of  the  plates,  but  a  little 
study  will  make  it  possible  to  distinguish  them  from  bacteria.     The 
bacteria  will  commonly  be  more  numerous  than  the  molds.     Similar 
plates  exposed  in  a  variety  of  locations  will  be  very  instructive  as 
indicating  the  abundance  of  bacteria  in  the  air. 

58.  Bacteria  in  Milk.     In  an  ordinary  flask  place  one  hundred 
cubic  centimeters  of  water  and  sterilize  by  steaming  for  two  hours. 
After  cooling  place  one  cubic  centimeter  of  ordinary  milk  in  the  flask 
and  mix  thoroughly  by  shaking.     Melt  three  tubes  of  gelatin  and  three 


284  BACTERIA,   YEASTS,  AND    MOLDS 

of  agar.  Into  one  tube  of  each  place  one  cubic  centimeter  of  the 
diluted  milk ;  into  a  second  tube  of  each  place  one  half  of  a  cubic 
centimeter,  and  into  a  third  a  single  drop.  Mix  thoroughly,  pour 
into  petri  dishes  as  usual,  harden,  and  set  aside  for  growth.  If 
possible,  count  the  number  of  bacteria  on  the  plates  and  estimate  the 
number  per  cubic  centimeter  (a  single  drop  is  about  one  fifteenth  of 
a  cubic  centimeter).  The  number  will  sometimes  be  too  large  to 
make  this  possible. 

59.  Effect  of  Temperature  upon  Milk.     Fill  six  test  tubes  full  of 
milk.     Place  two  of  them  in  an  ice  chest,  two  at  ordinary  room  tem- 
perature, and  two  close  to  a  stove  or  radiator  where  the  temperature 
is  very  warm.     Examine  at  intervals  of  three  or  four  hours  and  note 
the  time  at  which  the  tubes  become  sour  and  curdle.     Determine,  if 
possible,  whether  there  is  any  difference  in  the  appearance  or  smell 
of  the  curdled  milk  in  the  three  samples. 

60.  Effect  of  boiling  Milk.     Fill  two  test  tubes  one  third  full  of 
milk.     Place  one  of  them  in  water  and  allow  the  water  to  boil  briskly 
for  five  minutes.     The  second  one  is  not  to  be  boiled.     At  the  close 
of  the  boiling  plug  both  test  tubes  with  cotton  and  set  side  by  side 
in  a  warm  place.     Examine  each  day  and  notice  the  difference  in 
the  changes  that  take  place  in  the  milk.     One  sample  will  probably 
sour  quickly  ;  the  other  will  keep  very  much  longer  and  will  not  sour, 
even  after  many  days,  although  it  will  spoil.     Test  both  samples  with 
litmus  paper,  after  they  have  spoiled,  to  see  if  both  are  acid. 

61.  Growth  of  Bacteria  in  Milk.     Obtain  some  absolutely  fresh 
milk.     This  experiment  may  be  difficult  in  a  city  where  fresh  milk  is 
not  easy  to  obtain.     Place  one  cubic  centimeter  of  the  milk  in  one 
hundred  cubic  centimeters  of  boiled  and  cooled  water,  mix  thoroughly, 
and  then  with  a  clean  sterilized  pipette  place  one  cubic  centimeter  of 
the  diluted  milk  in  each  of  six  test   tubes  of  melted  agar  culture 
medium.     Mix  thoroughly,  pour  into  petri  dishes,  and  set  aside  for 
the  bacteria  to  grow.     Place  the  milk  at  a  warm  temperature  near 
a  radiator  for  six  or  eight  hours,  and  repeat  the  experiment,  making 
six  more  petri  dishes  in  the  same  way.     Set  all  aside,  and  after  the 
bacteria  have  grown  count  the  number  of  colonies  in  each,  thus 
determining  the  rate  of  multiplication  of  bacteria  between  the  first 
and  last  experiments. 


APPENDIX  285 

62.  Washing  of  Milk  Vessels.     Place  some  ordinary  milk  in  two 
test  tubes  and  set  aside  until  the  milk  sours.     Pour  out  the  milk  from 
all  the  test  tubes  and  wash  one  with  cold  water  and  the  other  with  hot 
water  and  soap.     Hold  the  tubes  up  to  the  light  and  notice  the  dif- 
ference in  the  cleanliness  of  the  two  test  tubes.     Now  fill  each  tube 
with  fresh  milk  and  set  aside  in  a  moderately  cool  place  and  notice  in 
which  of  the  tubes  the  milk  sours  first. 

63.  Vinegar   Bacteria.     Obtain   a  little   good  vinegar  containing 
some  of  the  mother  of  vinegar.     Put  a  bit  of  the  mother  upon  a  glass 
slide,  cover  with  a  cover  glass  to  spread  in  a  thin  layer,  and  study 
with  a  high-power  microscope. 

64.  Effect  of  Heat  in  sterilizing  Fruit.     Fill  four  test  tubes  about 
half  full  of  water.     In  each  place  a  few  small  berries,  like  blackber- 
ries or  blueberries,  or  pieces  of  cherry,  apple,  or  pear.    Plug  each 
tightly  with  cotton.     Put  one  aside  and  label  a.     Place  the  others 
in  cold  water  and  gradually  bring  the  water  to  a  boil.     Before  the 
water  boils  take  out  one  test  tube  and  label  it  b ;  take  out  a  second 
the  moment  the  water  boils  and  label  c ;  remove  a  third  after  the 
water  has  boiled  half  an  hour  and  label  d.     Set  all  tubes  aside  in  a 
warm  place  and  watch  for  several  days,  determining  which  are  suc- 
cessfully sterilized,  which  will  be  indicated  by  their  not  spoiling. 


INDEX 


Abscesses,  236. 

Acetic  acid,  132;  as  a  preservative, 
165;  in  bread,  92. 

Acidity,  effect  of,  upon  bacterial 
growth,  114;  effect  of,  on  mold 
growth,  38. 

^Ecidiomycetes,  12. 

Aerated,  bread,  88  ;  waters,  225. 

Aerobic  bacteria,  113. 

Air,  as  a  distributer  of  disease,  230 ; 
bacteria  in,  1 14  ;  its  effect  on  bac- 
terial growth,  112,  114;  on  mold 
growth,  34. 

Albumen,  125. 

Alcohol,  56,  198. 

Anaerobic  bacteria,  113. 

Anopheles,  216. 

Antenaria,  21. 

Antifermentine,  158. 

Antiseptic,  255 ;  use  of,  in  canning, 
178. 

Antitoxin,  250. 

Apollinaris  water,  225. 

Apple,  fermentation  of,  64. 

Ascomycetes,  12. 

Aspergillus,  19. 

Bacillus,  105. 

Bacon,  curing  of,  144. 

Bacteria,  classification  of,  103;  dis- 
tribution of,  114  ;  growth  of,  107  ; 
in  bread,  93 ;  in  yeast  cultures,  91 ; 
multiplication  of,  105 ;  relation  of, 


287 


to  air,  112;  shape  of,  102 ;  size  of, 
100,  101. 

Bacterial  growth,  results  of,  121, 
126. 

Bacterium,  105. 

Beans,  canning  of,  173,  174,  178, 
180;  soured,  166. 

Bedding,  treatment  of,  243. 

Beef,  dried,  144. 

Beer,  fermentation  of,  95 ;  home- 
made, 96. 

Berries,  drying  of,  146. 

Biscuits,  preservation  of,  142. 

Bitter  rot,  41. 

Black  rot,  41. 

Blood  poisoning,  203,  236. 

Blue  milk,  185. 

Blue  mold,  13;  fruit  of,  17. 

Boiling  as  a  preservative,  156,  161. 

Boils,  236. 

Books,  a  source  of  contagion,  244 ; 
molding  of,  33. 

Boracic  acid,  158. 

Borax,  use  as  a  preservative,  158, 
159,  178. 

Bread,  molding  of,  27  ;  raising  of, 
72,  86. 

Bread  raising,  purpose  of,  88  ;  rela- 
tion to  temperature,  89. 

Breathing,   a  source    of    infection, 

239- 

Brewer's  yeast,  77,  82,  83. 
Brie  cheese,  52. 


288 


BACTERIA,  YEASTS,  AND   MOLDS 


Brown  rot,  41. 
Bubonic  plague,  221. 
Budding,  10,  60;  fungi,  61. 
Butter,  flavor  of ,  6,  131,  198  ;  ruined 

by  bacteria,  134;  salting  of,  164. 
By-products,  127. 

Camembert  cheese,  52. 
Canned  foods,  value  of,  181  ;  mold- 
ing of,  26. 
Canning,  5,  169  ;  failures,  cause  of, 

i?5- 

Canning  in  factories,  177. 

Carbolic  acid,  as  a  disinfectant,  258 ; 
as  a  preservative,  1 58. 

Carbon  dioxide,  56, 

Carpets,  molding  of,  33. 

Casein,  125. 

Cats,  as  distributers  of  disease,  221. 

Cattle,  as  distributers  of  tuberculo- 
sis, 222. 

Celery,  234. 

Cellar,  use  of,  for  preserving  food, 

154. 

Cephalothecium,  21. 

Certified  milk,  186,  229. 

Charque,  144. 

Cheese,  flavor  of,  6,  198 ;  molding 
of,  27,  37;  poisoning,  199;  pres- 
ervation of,  in  brine,  164. 

Chills  and  fever,  214. 

Chloride  of  lime,  259. 

Cholera,  204,  220,  222,  223,  227,  238. 

Cider,  64,  71 ;  as  a  source  of  vine- 
gar, 133. 

Cloth,  molding  of,  33. 

Clothing,  disinfection  of,  243,  263. 

Coccus,  104. 

Cold,  as  a  disinfectant,  257;  as  a 
preservative,  148. 


Cold  storage,  148 ;  effect  of,  on 
molds,  37 ;  food  from,  1 50. 

Cool  temperatures,  devices  for,  155. 

Commercial  yeast,  impurities  in,  91. 

Compressed  yeast,  78 ;  keeping  of, 
80. 

Consumption,  212,  220,  232,  241, 
252. 

Contagion,  conditions  of,  213. 

Contagious  diseases,  i,  6;  distribu- 
tion of,  7,  208,  212. 

Corn,  canning  of,  173, 174,  178,  180. 

Corned  beef,  164. 

Corrosive  sublimate,  as  a  disinfect- 
ant, 258  ;  as  a  preservative,  158. 

Coughing,  a  means  of  distributing 
bacteria,  232. 

Crackers,  preservation  of,  142. 

Curtains,  in  sick  rooms,  121. 

Darkness,  effect  on   mold  growth, 

36. 

Death  of  bacteria  by  heating,  no. 

Decay,  i,  4,  128,  129;  advantages 
of,  130. 

Decay  of  fruit,  41,  49;  prevention 
of,  44. 

Decomposition  of  food,  126;  prod- 
ucts, 127. 

Deodorants,  259. 

Diastase,  86. 

Diphtheria,  204,  219,  227,  238,  239, 
241,  243,  244,  248,  250,  252. 

Dirt,  bacteria  in,  118. 

Disease  bacteria,  203 ;  vigor  of,  207. 

Disease  germs,  6,  122. 

Diseases,  caused  by  molds,  53 ;  cause 
of,  210,  212  ;  course  of,  205;  how 
produced,  203 ;  prevention  of,  7. 

Dishcloths,  138. 


INDEX 


289 


Disinfectants,  application  of,  261. 

Disinfection,  255. 

Distilled  liquors,  70. 

Distillery  yeast,  78,  79. 

Dried  yeast,  81. 

Drinking  water  a  source  of  disease, 

222. 

Drying  as  a  preservative,  33,  141. 
Dust,  in  the  schoolroom,  233 ;  in  the 

sick  room,  231. 

Eating  utensils,  treatment' of,  243. 
Eggs,  bacteria  in,  119;  preservation 

of,  164,  197. 
Elimination   of   germs   from   body, 

214. 

Epidemics,  210. 
Erysipelas,  236.  • 
Excreta,  242,  262;   as  a  source  of 

infection,  220. 

Fats  as  bacterial  foods,  1 24. 

Favus,  54,  236. 

Fermentation,  56  ;  checked  by  boil- 
ing, 68;  of  jellies,  65. 

Fermentative  industries,  95. 

Fermented  beverages,  57,  70. 

Fermenting  power  of  yeasts,  76. 

Figs,  163. 

Filtering  water,  224. 

Fish,  poisoning  from  eating,  199  ; 
preserving  of,  145,  163. 

Fission,  10,  106. 

Flagella,  103,  105. 

Flavors,  from  bacterial  growth,  127, 
130;  of  butter,  6;  of  cheese,  6; 
produced  by  yeasts,  88. 

Fleas  as  distributers  of  disease,  221. 

Flies  as  distributers  of  disease,  221. 

Floors,  bacteria  on,  118. 


Flour,  molding  of,  27,33  >  preserved 

by  drying,  142. 
Food  as   a  distributer   of  disease, 

234- 

Foods,  bacteria  in,  118;  of  bacte- 
ria, 121, 124;  preservation  of,  139; 

ruined  by  bacteria,   134;  use  of, 

while  fresh,  140. 
Formalin,    158;    as   a  disinfectant, 

260,  264,  266. 
Freezine,  158. 
Freezing  of  food,  149. 
Fresh   air,   need   of,   251  ;    in   sick 

room,  265. 
Fruits,  canning  of,  172,  180;  decay 

of,  40,  42,  119;   drying  of,  146; 

moisture  in,  32  ;  packing  of,  46 ; 

wrapping  in  paper,  47. 
Fungi,  9,  10. 

Gamy  flavors,  118,  130,  198. 
Garbage,  135;  cans,  137. 
Germicide,  255. 
Gluten,  125. 

Gorgonzola  cheese,  31,  52. 
Grippe,  220,  239. 

Hair,  a  lodging  place  for  bacteria, 
245  ;  disinfection  of,  263. 

Hams,  curing  of,  144,  164. 

Hands,  disinfection  of,  262. 

Hangings  in  sick  rooms,  121. 

Heat,  as  a  disinfectant,  256;  as  a 
preservative,  156;  killing  molds 
by,  37  ;  required  for  canning,  172, 
174. 

Hip  disease,  252. 

Home  brewing  of  yeast,  83. 

Hops,.as  a  preservative,  168  ;  use  of, 
in  yeast,  84. 


290 


BACTERIA,  YEASTS,  AND  MOLDS 


Ice  a  source  of  disease  germs,  226. 

Ice  chest,  151 ;  cleaning  of,  153;  ef- 
fect of,  on  molds,  36 ;  use  of,  in 
preserving  milk,  190. 

Ice  cream,  202,  205. 

Immunity,  248. 

Impurities  in  yeast,  91. 

Insects  as  distributers  of  disease, 
221. 

Intestines,  bacteria  in,  119. 

Invasion,  means  of,  235. 

Isolation,  necessity  for,  241. 

Jellies,  fermentation  of,  65;  preser- 
vation of,  163;  protection  of,  25. 

Kefir,  99. 
Kumiss,  98. 

Lactic  acid,  a  preservative,  166  ;  in 

bread,  92. 

Lactic  bacteria,  184. 
Lakes,  bacteria  in,  116. 
Leather,  molding  of,  33. 
Leaven,  73. 
Legumen,  125. 
Lettuce,  234. 
Light,  as  a  disinfectant,  257  ;  effect 

of,  on  bacteria,  112. 
Limburger  cheese,  131. 
Lockjaw,  236,  237,  257. 

Malaria,  213,   252;   cause  of,   214; 

distribution  of,  216. 
Maple  sugar,  fermentation  of,  65. 
Marmalades,  163. 
Mattresses,  264. 
Mazoon,  99. 
Measles,    212,    213,    219,    230,  232, 

236,  239,  241,  248. 


Meats,  canning  of,  179,  180;  mold- 
ing of>  33- 

Micrococcus,  104. 

Microorganisms,  and  disease,  6  ;  and 
preservation  of  food,  2  ;  classes 
of,  8. 

Microsporon,  53. 

Mildew,  28,  32,  34. 

Milk  as  a  distributer  of  disease, 
222,  227  ;  methods  of  guarding 
against,  228. 

Milk  bacteria,  182  ;  effect  of,  on  milk, 
183. 

Milk,  condensed,  163 ;  drying  of, 
145 ;  fermented,  98  ;  from  gro- 
ceries, 187;  from  milkmen,  187; 
poisoning  from,  199;  preservation 
of,  185  ;  preserved  at  low  temper- 
atures, 190;  sources  of,  185; 
vessels,  188. 

Mince-meat,  167. 

Mineral  substances,  9. 

Moisture,  and  decay,  45;  effecting 
mold  growth,  26,  32 ;  in  fruit, 
46;  required  for  bacteria,  113. 

Mold  growth,  results  of,  28. 

Molding,    prevention   of,   by   heat, 

37- 
Molds,  color  of,  15;   fruit  of,    17; 

general   nature   of,  12;   meaning 

of  the  term,  n  ;  structure  of,  16; 

wholesomeness  of,  30. 
Moldy  bread,  bacteria  in,  119. 
Monilia,  22,  41. 
Mosquito  netting,  218. 
Mosquitoes  and  malaria,  216. 
Mother  of  vinegar,  132. 
Mouth,  bacteria  in,  119;  a  source  foi 

entrance  of  germs,  238. 
Mucor,  14,  1 8,  21. 


INDEX 


29I 


Multiplication  of  bacteria,  105 ; 
rapidity  of,  107  ;  relation  to  tem- 
perature, 109. 

Mushrooms,  10. 

Mussels,  drying  of,  145. 

Mustiness,  29,  32. 

Mycelium,  17. 

Myosin,  125. 

Night  air,  218,  251. 
Nurses,  care  of  person  of,  245 ;  disin- 
fection of,  262. 

Odors  from  bacterial  growth,  127. 

Organic  substances,  9. 

Ovus,  67. 

Oxygen,  relation  of  bacteria  to,  128. 

Paper,  molding  of,  28. 

Parasites,  122,  203. 

Pasteur  filter,  224. 

Pasteurization  of  milk,  5,  193,  229. 

Pasteurizing  apparatus,  195. 

Pathogenic  bacteria,  6,  203. 

Patient,  disinfection  of,  262  ;  care  of 

person  of,  245,  262,  265. 
Peas,    canning   of,    173,    174,    178, 

1 80. 

Pemmican,  143. 
Penicillium  glaucum,  13,  15. 
Phosphorescence  of  food,  1 52. 
Physical  vigor  a  protection  against 

disease,  250. 

Pickles,  165;  molding  of,  27. 
Plums,  163. 
Poison   secreted   by  bacteria,    129, 

199. 
Poisoning    from    cheese    and    ice 

cream,  199. 
Pork,  preservation  of,  164. 


Preservaline,  158. 
Preservation  of  food,  2. 
Preservatives,  in  canning,    179;  in 

milk,  191 ;  poisonous,  157  ;  use  of 

condemned,  161. 
Preserved  foods,  140. 
Preserves,  163. 

Protection  of  food  from  mold,  24. 
Proteids  as  bacterial  food,  121,  125. 
Ptomaine  poisoning,  201. 
Ptomaines,  199. 
Putrefaction,  4,  119,  128,  129,  134; 

at  low  temperatures,  152  ;  caused 

by  molds,  30;  of  milk,  184,  185. 

Quick  biscuit,  89. 

Radishes,  234. 

Raising  of  bread,  87. 

Raisins,  146,  163. 

Rancidity  due  to  bacteria,  124. 

Rats  as  distributers  of  disease,  221. 

Reaction,  effect  of,  on  molds,  38; 

effect  of,  on  bacteria,  114. 
Red  milk,  185. 
Reservoirs,  bacteria  in,  116. 
Resistance  against  disease,  206. 
Rhubarb,  canning  of,  172. 
Ringworm,  52,  236,  244. 
Rivers,  bacteria  in,  116. 
Rod-shaped  bacteria,  105. 
Rooms  infected  with  molds,  54. 
Roquefort  cheese,  6,  28,  31,  52. 
Rotting.     See  Decay. 
Rusts,  10. 

Saccharomyces,  62,  79. 

Salads,  167. 

Salicylic  acid,  158. 

Salt  as  a  preservative,  164. 


292 


BACTERIA,   YEASTS,  AND   MOLDS 


Salt  raising  of  bread,  75. 

Salt  used  in  drying  meat,  144. 

Sanitary,  dairies,  186;  milk,  229. 

Saprophytes,  122,  124,  203. 

Sarcina,  104. 

Sauerkraut,  166,  198. 

Sausages,  167. 

Scarlet  fever,    212,    213,  219,   221, 

227,  230,  236,  241,  244,  248. 
Schoolrooms,  bacteria  in,  115. 
Scotch  barms,  76. 
Scrofula,  252. 
Scurvy,  165. 

Secretions  from  bacteria,  129. 
Seeds,  preservation  of,  141. 
Seltzer  water,  226. 
Septicaemia,  203. 
Sewage,  116,  222,  246;  farms,  234; 

gas,  247. 

Shellfish,  drying  of,  145. 
Sick    room,    disinfection   of,    264; 

treatment  of,  245. 
Sink,  care  of,  138. 
Siris,  67. 
Skin,    a    means   of  invasion,   235; 

a  protection,  236;  diseases,  230; 

value  of  clean,  47. 
Slacked  lime,  260. 
Slimy,  bread,  93;  milk,  184. 
Smallpox,  219,  221,  230,  236,  241, 

251,  252. 
Smuts,  10. 

Soil,  bacteria  in,  117. 
Sour  bread,  92. 

Sour  milk,  bacteria  in,  119,  184. 
Souring  of  foods,  4. 
Sparkling  wines,  96. 
Spherical  bacteria,  104. 
Spices  as  preservatives,  167. 
Spiral  bacteria,  105. 


Spoiling  of  foods,  i,  2,  118. 

Spontaneous  fermentation,  64. 

Sporangia,  19. 

Spores,  17,  37,  106,  256;  germina- 
tion of,  22;  of  yeast,  62;  resist- 
ance of,  to  heat,  107,  in,  172. 

Spring  houses,  155. 

Spring  water,  bacteria  in,  116. 

Sputum  a  source  of  infection,  220, 
232. 

Starch  as  bacterial  food,  121,  124. 

Sterilization,  in,  229;  before  can- 
ning, 171;  of  milk,  5,  191,  192; 
purpose  of,  192. 

Stilton  cheese,  31,  52. 

Stomach,  bacteria  in,  119. 

Streptococcus,  104. 

Stysanus,  21. 

Sugar,  a  bacterial  food,  121,  124; 
as  a  preservative,  66,  162 ;  in 
fruits,  146. 

Sulphur  as  a  disinfectant,  260,  265. 

Summer  diarrhea,  200,  227. 

Sunlight  as  a  disinfectant,  257. 

Sweeping,  120. 

Tassajo,  144. 

Temperature,  effect  of,  on  decay  of 

fruit,  48 ;  effect  of,  on  milk,  189 ; 

effect  of,  on  molds,  36 ;  relation  of, 

to  bread  raising,  89  ;  relation  of, 

to  growth,  109. 
Tetanus,  237. 
Toadstools,  10. 
Tomatoes,    canning    of,    172,    174, 

1 80. 

Torula,  62. 
Toxic    poisoning    not     a     disease, 

205. 
Toxins  produced  in  the  body,  204. 


INDEX 


293 


Transportation   of    disease    germs, 

220. 

Traps,  246. 
Trichina,  145. 
Trichophyton,  53. 
Tuberculosis,     212,    222,    227,    232, 

235,  238,  239,  243,  251,  252. 
Typhoid  fever,   102,  212,  220,  221, 

222,  227,  238,  243,  252. 

Unfermented  grape  juice,  70. 
Unleavened  bread,  73. 
Utility  of  molds,  51. 

Vaccination,  248. 

Vacuoles,  60. 

Vegetables,  drying  of,  146  ;  preser- 
vation of,  155. 

Vinegar,  6,  72,  131,  198  ;  as  a  pre- 
servative, 165;  eels,  134. 

Water,  as  a  distributer  of  disease, 

222;  bacteria  in,  115. 
Wells,  a  source  of  infection,  222; 

for  preserving  food,   155. 


Wholesomeness  of  bacterial  prod- 
ucts, 197. 

Whooping  cough,  212,  213,  219,  232, 
239,  241. 

Wild  yeasts,  58,  63,  65,  70. 

Wines,  homemade,  71  ;  method  of 
making,  70  ;  sparkling,  96. 

Wood,  decaying  of,  51. 

Wounds,  treatment  of,  238. 

Wuk,  67. 

Yeast,  as  a  cause   of  bitter  milk, 

68  ;  as  an  enemy,  68  ;  as  a  friend, 

69  ;   brewk,   83  ;    cultivated,   76  ; 
differentSJdnds  of,  77  ;  discovery 
of,  50 ;  distribution  of,  63  ;  food  of, 
66  ;  growing  state  of,  60  ;  in  bread 
making,  74 ;  method  of  obtaining, 
75  ;  powder,  82 ;  preparations,  79  ; 
selection  of  best  species  of,  78 ; 
species  of,  61 ;    structure  of,  59; 
used  as  a  source  of  alcohol,  69 ; 
as  a  source  of  carbon  dioxide,  7  2  ; 
waste  as  a  food,  67. 

Yellow  fever,  214,  219. 


ANNOUNCEMENTS 


.05 


EXPERIMENTAL    DAIRY 
BACTERIOLOGY 

By  H.  L.  RUSSELL,  Dean  of  the  College  of  Agriculture,  University  of  Wisconsin, 

and  E.  G.  HASTINGS,  Assistant  Professor  of  Agricultural 

Bacteriology,  University  of  Wisconsin 

Newizmo.   Cloth.    147  pages.   Illustrated.  List  price,  $1.00;  mailing  price,  $i. 

THE  purpose  of  the  course  here  outlined  is  to  train  the 
student  in  those  bacteriological  processes  that  are 
necessary  for  him  to  comprehend  thoroughly  before 
he  is  in  a  position  to  appreciate  the  relation  of  microorganisms 
to  dairy  processes.  This  work  is  of  fundamental  importance 
to  the  student  who  wishes  to  learn  the  nature  of  the  biological 
changes  going  on  in  milk  and  its  products,  whether  he  is  con- 
cerned purely  with  the  practical  sideof  dairying  or  is  interested 
in  the  cognate  work  of  dairy  chemistry  or  dairy  bacteriology. 

The  attempt  has  been  made  to  keep  the  scope  of  this  work 
within  the  realm  of  dairy  bacteriology,  and  not  to  encroach 
upon  the  field  of  dairy  manufactures. 

The  methods  presented  are  believed  to  be  the  best  in  use 
at  the  present  time.  A  committee  of  the  American  Public 
Health  Association  now  has  under  consideration  the  formu- 
lation of  standard  methods  for  milk  analysis,  but  these  have 
not  as  yet  been  published.  The  methods  of  media  making 
are  those  recommended  by  the  Laboratory  Section  of  the 
American  Public  Health  Association,  and,  while  more  com- 
plicated than  those  usually  described  in  text-books,  are  surely 
more  desirable  in  establishing  uniform  methods. 

A  plate  counter,  which  will  be  found  of  much  practical 
value  and  convenience,  will  be  provided  free  of  charge  with 
each  copy  of  this  book. 

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